


In the Name of Science

by dimetrodon



Category: Undertale (Video Game)
Genre: Angst, But also plot, Eventual Romance, Eventual Smut, F/M, Fluff, Fluff and Angst, Friends to Lovers, Gaster is a cinnamon roll, Gen, Goopy W. D. Gaster, Hurt/Comfort, I'll update the tags as I go, Mute!Gaster, Reader Is Not Frisk (Undertale), Reader-Insert, Selectively Mute Frisk (Undertale), Slice of Life, Slow Burn, Swearing, They’re both nerds ok, don't worry friends, he needs a hug, he won't be goopy forever though, like the slowest of burns, not dadster, reader has female pronouns, reader is a scientist, there IS a plot
Language: English
Status: In-Progress
Published: 2019-01-08
Updated: 2019-02-25
Packaged: 2019-10-06 02:04:56
Rating: Mature
Warnings: No Archive Warnings Apply
Chapters: 15
Words: 41,763
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/17336624
Author URL: https://archiveofourown.org/users/dimetrodon/pseuds/dimetrodon
Summary: When a human scientist gets permission to visit the Underground four years after monsters resurfaced, she jumps at the chance to conduct her research.She didn't expect to find someone down there.She didn't expect to embark on an incredible journey to find this stranger's missing pieces, and put him back together.And she certainly didn't expect to find love along the way.*Updated twice a week!





	1. Permission Granted

**Author's Note:**

> Hi Readers! Welcome to my first fanfic!
> 
> Hopefully people read this, and like it. 
> 
> Any comments and constructive criticism are welcome (like I said, this is my first fanfic, so I think I've got a long way to go in terms of writing).
> 
> Tumblr (to talk to me, ask me questions, all that good stuff): https://dimetrodonao3.tumblr.com/

_Shit._

You were so screwed.

You launched yourself from the comfort of your toasty bed at the sight of the numbers that lit your phone’s screen. 9:16. You had fourteen minutes to get yourself ready, get your things together, and run to work.

You stumbled to your closet and pulled out the first pair of jeans you saw, and a large grey sweater. As you tugged the sweater on, you blindly entered the living room, making a beeline for the small fish tank against the wall. A smile graced your features at the sight of your lone companion: May, your small catfish. You shook a little food into her tank, before speeding to the bathroom to brush your teeth.

When you emerged, you grabbed your laptop off the kitchen counter, an apple from the fridge, some of your work papers from the dining table, and your lab coat from the hook by the front door. You wrenched the door open and began the short run to the university where you studied and researched.

You were in the final year of your Master’s research degree as an evolutionary biologist. When you’d finished your undergrad degree, you’d been a little lost, unsure of the direction you wanted to take your life in. But since monsters had emerged from beneath Mount Ebott four years ago, the choice couldn’t have been any clearer.

This race of people, their evolutionary history, and how the biological and magical components of monsters interacted absolutely fascinated you. You understood then that humanity (and indeed monsterkind) were at the forefront of a major scientific breakthrough. And you’d be damned if you weren’t going to be a part of it.

So that was how you’d ended up here, doing a research degree at a university just an hour’s drive from the mountain and the Underground itself. The last four years felt like a blur – you and your colleagues had made a lot of progress on understanding the evolutionary links between humans and monsters, but there were still so many gaps in knowledge to be filled. Many of which you suspected could be solved with a visit to the Underground – you needed a deeper understanding of the environmental conditions monsters lived under, as well as samples of vegetation and water bodies.

Unfortunately, human access to the Underground was still tightly restricted, and although you’d had an application for permission to enter lodged to the King of Monsters for some time now, you had yet to hear back. So for now, you just had to make the best of what you had.

You ended up making it to the lab only a couple of minutes late. You scanned your ID at the door, buzzing yourself in. To your mild surprise, you noticed a familiar figure standing by your research area.

You and Doctor Alphys had neighbouring research labs, and after a few months limited to awkward small talk and avoiding eye contact, you had eventually worked up the courage to befriend the shy scientist. It was nice to finally have someone to eat lunch with and talk to at work. You had a feeling Alphys didn’t have many friends around here either.

“Oh, h-hey, Y/N!” Alphys’ features lit up as she saw you approaching.

“Hey Alphys!” you responded with a grin. “Don’t tell me you’ve run out of burettes again?” Last week Alphys had sheepishly showed up at your lab, begging for a burette after accidentally sweeping a table of glassware onto the floor with her tail (after being startled by her girlfriend’s sudden and... _loud_ appearance).

Alphys ducked her head slightly, clearly embarrassed. “N-no... Actually! I have some good news for you.” She beamed excitedly, pulling a folded piece of paper from the pocket of her lab coat and holding it out to you. Intrigued, you plucked the paper from her outstretched claw, and unfolded it.

Within a second of scanning the paper’s contents, you knew exactly what this was. You had Royal permission! You were actually allowed to enter the Underground!

Against your own will, a squeak of excitement left your lips as you hopped on the spot for a second. “I can’t believe it! Finally! I seriously thought I was never going to get in!”

Alphys let out a giggle at your obvious ecstasy. “It takes a l-long time to do all the security checks and everything... But! Obviously you’ve been deemed s-safe. Congratulations, Y/N!” 

You responded with sincere thanks as you began bustling around your lab, gathering up all the field equipment you’d need. The work you’d planned on doing today could wait.

A look of confusion passed Alphys’ features. “W-wait, you’re going now?” she stammered.

“Of course!” You turned your head, flashing a smile in her direction. “Alphys, I’ve been waiting for this day for three and a half years! How could I not go now?”

Alphys nodded. “I w-would offer to go with you, but I have several deadlines I need to meet today... Unless! You want to wait until tomorrow? I-I could come with you then, help you find your way around?”

“I really appreciate the offer,” you responded, “But I honestly think I’d drive myself nuts if I waited another day. I definitely wouldn’t be able to get any work done today.” It was true. You were practically giddy with excitement as it was.

The lizard monster grinned, “Y-yeah, I understand the feeling! Well, I’ll leave you to it then.” She left your lab with a small wave, which you returned.

You made a mental list of what you had gathered. _Sample containers, water-testing kits, forceps, gloves, labels, and maps of the Underground._ That should be all you really needed, for a first cursory visit anyway. You also had your phone, which you could use to take pictures of the various strange environmental systems down there.

Nodding absently to yourself, you packed all the equipment into a field backpack, and headed off with a spring in your step.

* * *

 

The drive to Mount Ebott was a relatively peaceful and uneventful one. The further you strayed from the city, the more serene your surroundings. Gentle hills blanketed with lush vegetation rolled past, and the azure sky overhead was totally devoid of clouds.

Then suddenly, Mount Ebott itself. It split the sky like an axe, towering above everything around it. You recalled the first time you had seen the behemoth – on a live news broadcast, on the fateful day when monsters had resurfaced.

You vividly remembered the chaos of that day (and indeed many of the following months). The confusion and wonder as humans fought to get a glimpse of the so-called race of monsters that had emerged from beneath the mountain. The animosity of so many humans, who had been enraged at the prospect of having to share their world and their lives with these creatures. The gaping divide between monsters and humans.

The divide was still present, four years later, unfortunately. But it was nowhere near as wide as it was then. Progress was slow, but thankfully monsters were becoming more and more integrated into society. As monsters were accounted for legally and politically, the initial chaos and insanity died down. But a lot of the underlying prejudice and racism still remained.

You were drawn from your thoughts as you approached the military-protected border. A tall gate lined with barbed wire obstructed your path. You slowed your car right down and rolled down your window as a soldier approached. 

“ID?” she asked in a blunt, no-nonsense tone. Wordlessly, you rummaged around your bag and handed her your license. She took it into the gatehouse beside the road.

Suddenly, a pit of nervousness churned in your stomach. What if you weren’t in the system yet? You had only just gotten permission this morning, right? Should you have waited a couple days or something? You squirmed in your seat.

After what seemed like an eternity, the soldier emerged from the gatehouse and approached your car. “You’re good to go,” she handed your license back, and all the tension in your body evaporated. “Be careful down there.” She warned.

You nodded an affirmative and started your car again as the gate before the mountain rolled aside.

* * *

The cave gaped before you; a tunnel in complete darkness, of indeterminate length. You pulled out your phone to snap a picture for later reference.

You were beginning to wish you’d waited until tomorrow and taken up Alphys’ offer to show you around.

But you steeled your nerves. You were being ridiculous. This was a once in a lifetime opportunity! This trip could be what allowed you to complete your research and fill in the gaps in monsters’ known evolutionary history.

Flicking on your phone’s torch, you began the descent.

After a few terrifying minutes of stumbling down into darkness, light began to pervade your field of vision. But from where? You glanced up to the cave’s low ceiling.

_Of course._

The rocky surface above you was sprinkled with what looked like some kind of bioluminescent moss, emitting faint yellow light. You snapped another picture and decided to collect a sample to analyse in the lab later.

As you resumed your journey, you noticed that the abundance of the moss increased the further down you went. The passage became brighter, and you no longer needed your phone’s torch.

In the distance ahead, you noticed that the passage came to an end, where a massive golden door lay nestled amongst the rocks. Eager now, you rushed towards the door, and struggled to pull it open and slide through. 

You found yourself in a cavernous hall with enormous windows lining gold-gilded walls, and a floor so polished you could see your own reflection. _The Judgement Hall_ , you recalled from the maps you had studied. You pulled one of said maps from your bag to confirm where you were headed next.

It seemed that if you kept heading west, you would arrive in Hotland outside the Core. You wanted samples from the three major ecosystems in the Underground – Snowdin, Waterfall, and Hotland – to give yourself an understanding of the environmental conditions under which monsters had lived and adapted to. The logical way to approach this would be to just keep heading west – starting at Hotland, moving on to Waterfall, and ending in Snowdin. With that plan in mind, you folded the map and tucked it back into your bag and continued through the hall.

The castle itself wasn’t hard to navigate, and you soon found yourself in an elevator which would take you outside the Core. As the silver doors slid open, you were met with a rush of hot, dry air. _Maybe jeans and a sweater weren’t the best choice._ Rolling your sleeves up to your elbows, you stepped out onto the cracked, red earth beneath your feet, and examined your surroundings.

The area was fairly barren – no substantial organic matter as far as you could tell. Nevertheless, you bent down to begin taking some samples, and snapped a few photos of your surroundings too. You were a little miffed that there was no vegetation here as far as you could see, but you supposed it made sense given the unbearable heat.

Your eyes were drawn to the edge of the platform you were on – a sea of lava roiled far below you. Against your better judgement, you sat on the ledge, dangling your legs over the edge. Already, the heat seemed to be sinking into your bones, making your blood sluggish and your muscles heavy. 

As you cast your eyes downward, you noticed several layered rock platforms jutting from the edge of the cliff beneath you. Intrigued, you leaned over further to look more closely. Something grey caught your eye – it was a small object, no larger than an apple, on a platform a few metres below you.

_Hold on – is it... moving?_

Surely enough, the grey mass seemed to be shifting and writhing before your eyes. You realised that it was probably something organic – something you should definitely get a sample of.

You shuffled off the ground, dropping to a platform directly underneath you. _So far, so good._ On your hands and knees, you crawled across the platform so that you were directly above the strange grey object.

It was definitely moving. It was stationary in its position on the platform, but its surface was aggressively pulsing with waves and valleys.

Though it was directly beneath you, it was a couple metres’ drop – you couldn’t just jump down without risking falling to a premature death. Taking a deep breath, you dangled your legs over the platform, then dropped yourself so that you were clinging by just your hands. Your feet scrambled on the wall for footholds, until you reached a somewhat stable position.

One by one, you moved your feet further down to other footholds, reluctantly relinquishing your hands’ grip on the platform in favour of little outcroppings of the cliff face. You were almost there.

Suddenly, the rock your left foot rested on gave way. You panicked, attempting to grab something, anything, on the vertical surface. But to no avail. You fell through the air, and your side struck the platform hard. The impact would have sent you rolling off the edge into the sea of lava had it not been for a jagged piece of rock jutting from the platform, which you managed to grab at the last second.

Breathing harshly, you struggled to calm yourself. The edges of your vision had darkened, and you could hear a faint sound – _like static_ – over the pounding of your heartbeat. Must be a result of the shock. You slowly hauled yourself up.

The grey object pulsed before you. You were just a few steps from it now – this thing you’d recklessly risked your life for. Gritting your teeth, you stepped towards it, prepared to take a sample.

When you did, though, your vision tunnelled further and the static hum became louder. You wouldn’t let that stop you. Determined, you walked right up to it, ignoring your limited field of vision and the droning in your ears.

Until you saw it.

You stopped dead in your tracks. You dared not take another step forward.

A towering figure loomed over you. It was black – blacker than any night you had ever seen – and its shape was amorphous. Almost like the grey object which it stood behind, its figure seemed to shift and change before your eyes. Except for its... face? A stark white oval in the midst of the roiling blackness, with what looked like large, misshapen eye sockets and a gash of a mouth.

_What the hell had you gotten yourself into?_

**Notes for the Chapter:**

> Well, that's chapter one! Hope everyone liked it. 
> 
> Sorry if it was a little dull/slow - I wanted to introduce some background and stuff before launching into plot stuff :D
> 
> Again, any comments/constructive criticism are welcome! 
> 
> (also if anyone has any other suggestions for the summary of this story, let me know, because I don't love the one I have up at the moment)


	2. Strangers

**Notes for the Chapter:**

> Hey everyone! 
> 
> Thank you so much to everyone who read the first chapter! I'm glad people are enjoying it so far. 
> 
> I hope I've done an ok job of writing Gaster - let me know what you guys think!
> 
> Any comments and constructive criticism are welcome :D
> 
> Tumblr (to talk to me, ask me questions, all that good stuff): https://dimetrodonao3.tumblr.com/

You were frozen.

Your blood was ice, your muscles were locked in place. Static roared in your ears and darkness shrouded your vision. Your brain was scrambling to form a response to the creature that had appeared before you.

Before your body could catch up with your mind’s instinct to _run – get the hell out of here_ , your eyes caught movement before you. Amidst the figure’s vacuous blackness were two white... hands? They didn’t seem to be quite _solid_ , just like the rest of the creature, and had holes where the palms should have been. Nevertheless, they were definitely hands. 

And they were moving; frantically forming shapes and signals. _Sign language?_ You had never learned sign language – you’d never needed to – so even if that was what it was doing, you had no way to understand it. But then your eyes slid back to the figure’s face. It – _he?_ – wore an expression you could only describe as distressed. His strange eyes seemed to be pleading with you.

You felt your fear slowly evaporate as you realised that if this thing wanted to hurt you, it would have and could have done so already. You took a deep breath and tried to speak as steadily as you could. “Are you... what are you?” Despite your efforts, your words came out shaky and breathless. The figure began to rapidly sign a response.

Now you felt stupid – asking a question to someone you couldn’t understand. “Sorry, I-I don’t understand.” The figure lowered his head, frustrated. “Oh, hold on a second!” you blurted, rummaging around in your backpack until you found what you were looking for.

You pulled out your notebook and pencil, and cautiously held them out to him. One of his hands slowly came forward, and gingerly took them from you, nodding in thanks. You watched, intrigued as he flipped the notebook open, wrote something inside, and then turned it to show you.

**Hello, my name is W.D. Gaster. I am sorry if I startled you – my appearance must be unusual to you. To answer your question; I am a monster.  
** **Forgive me for asking, but are you a human? I only ask because I have never seen an adult human before.**

_Never seen an adult human before?_ That could only mean that this monster had been in the Underground for the last four years – he must not have been to the surface yet. “It’s nice to meet you, Gaster,” your voice was less shaky, “My name’s Y/N. And yes, I’m a human.” He nodded in acknowledgement and began writing something else.

**I’m curious – what would bring a human to the Underground?**

You lit up at the prospect of talking about your research. You figured there was no harm in it – this monster didn’t seem so sinister anymore. “Well, I’ve got special permission from the King to come down here to take samples and scope out the different ecosystems here. I’m researching monsters’ evolutionary history, how that ties into other species’ evolution, and how magic factors into your biology. I’ve made some groundwork, but I really needed to actually get down here and get an understanding of the environment and the selection pressures you might have faced, among other things.” Gaster’s face seems to light up, as he scribbles something into the notebook.

**Are you a scientist, then? A biologist?**

You nodded eagerly. “Yes, exactly!” He smiled at you, before going back to write in the notebook. You were starting to feel bad that he had to write down all his responses to you. You really should learn at least some basic sign language, if only to not embarrass yourself like this again in the future.

**I was a scientist, as well. Not a biologist, though. I was more of a physicist, myself.**

_Was_ a scientist? You decided not to ask, though you did wonder. You couldn’t believe your luck, though – of all the people to run into down here, you happened to run into a former scientist! A physicist, but still – he might be able to tell you about the grey thing that had brought you down here in the first place.

You were starting to think that perhaps it was your proximity to the grey thing, and not Gaster, that was causing the droning static and tunnel vision. Although, come to think of it, Gaster had only appeared to you when you stepped close to the grey object. Maybe he was connected to it somehow?

 “I was wondering...” you began, somewhat hesitantly, “That grey thing,” you gestured towards it with a hand, “is it biological? I came down here because I saw it moving and I wanted to try and get a sample.” At the mention of the grey object, Gaster’s entire demeanour shifted. He cast his gaze down to it, his mouth drooping into a frown, his form slumping slightly. You started to think you shouldn’t have mentioned it. 

He hesitated for a second, before going to the notebook.

**It is not biological, per se. Taking a sample likely would not yield any results.**

You were confused – _how is it moving, then?_ – but you decided not to press. Instead, you changed the direction of the conversation. “Ok. Thanks for letting me know. You said you’ve never seen an adult human before – does that mean you haven’t been to the surface yet?” You had thought the Underground would be totally empty – as far as you knew, all monsters had relocated to the surface, wanting to be free.

He gives his head a slow shake, before responding.

 **I cannot leave this place. I must remain in the Underground.  
****On another note – have you collected samples from Waterfall and Snowdin already? Or do you have yet to visit there?**  

More and more questions were popping up in your head – _why can’t he leave the Underground?_ – but you sensed that this was a sensitive subject, so you let them slide. He seemed a little wary of you (as you were of him), but you thought that maybe you could earn his trust a little and get some much-wanted answers from him. Plus, he was a scientist too! He might have some important insights into the areas you would be studying and the samples you should collect.

Not to mention, he seemed... lonely. When you’d first seen him, and were visibly terrified, he had frantically trying to tell you that he wasn’t a threat. To stop you from bolting away. Not that you’d understood what he was saying, but still. And he had been in the Underground (presumably by himself) for the last four years, while everyone else moved to the surface. You would feel bad just leaving him here.

“No, I haven’t been there yet. I do need some initial samples that I can take back to the lab for analysis. Hotland was my first stop.” You paused for a moment, considering your next words carefully. “Would you... Do you want to come with me?” Gaster’s eyes widened, and his features seemed to brighten as he nodded to you, before pausing, and turning to the notebook.

**I would love to join you while you collect your samples. However, my movement is somewhat restricted. I cannot move more than a few steps away from ~~my~~ the grey object.**

You were burning to know what the grey thing was at this point, and why he was so strongly connected to it. You couldn’t help yourself and let a couple of questions slip out. “Is the grey thing the thing that’s making that static noise? And darkening my vision? Is that happening to you, too?” He looked upset for a moment before he responded.

**It likely is the cause. However, I am not affected by it the way you are. I suspect other people would be.**

You nodded as if you understood, even though his answer had raised more questions than it answered. “You can’t move away from the grey thing... and I’m assuming you can’t just pick it up and take it with you?” You asked. He simply shook his head dejectedly in response, moving towards the grey thing and bending down as if to pick it up, but when his hand should have met its shifting surface, it simply passed through. Your mind was spinning – so Gaster could touch and hold the notebook and pencil, but he couldn’t touch this thing he seemed so strongly connected to? It didn’t make any sense. Maybe no one could touch it.

You decided to test this theory. Also, you couldn’t help but wonder how long he had been stuck here, alone, considering he couldn’t leave the grey thing or move it himself. You felt like you should at least see if you could move it. “... Can I pick it up? So you can move around, I mean. I could take it with me to go to Waterfall and Snowdin so you can come with me.” You were starting to ramble. “Only if you still want to. Is it even possible for me to touch it?” You forced yourself to stop talking.

Gaster looked a little stunned but paused in what looked like contemplation. You wondered if you had said something stupid or offended him in some way. You really hoped not.

**You should be able to touch it. I would be honoured to join you, if you are willing to take me with you.**

You breathed a silent sigh of relief. So, you hadn’t said anything outrageously offensive or uneducated. You faced Gaster with a bright smile. “Alright then,” you clapped your hands together before bending down to pick up the grey thing. Sure enough, you touched it without a problem. It continued rippling and roiling, which felt unlike anything you’d ever touched before, and it was cool and metallic against your hands. You unzipped your backpack, and with utmost care, placed the grey orb safely inside.

Your focus shifted back to Gaster. “Shall we head off?” His mouth was curved into hopeful smile as he curled one hand into a fist, raised it, and made a knocking motion. _Was that sign language for ‘yes’?_ You assumed so. 

You turned to face the vertical rock face and steeled yourself. Climbing back to the top would be tough, but you had to get back up there somehow. There were no jutting rock platforms in your immediate reach, so you had to lock your hands onto small indents in the wall, slowly making your way up to the first platform, about a metre out of your reach. You hauled yourself onto the platform, panting. The extreme heat and dryness here made physical exertion that much more painful. The fact that you were wearing jeans and a sweater didn’t help.

You took a break for a minute, kneeling on the platform. Somehow, Gaster was standing beside you. _Did he... climb up?_ He didn’t look tired at all. In fact, he just looked concerned about the state you were in.

Luckily, there was another platform above you just within your reach. You stood, and grasped it with both hands, planting your feet on the vertical rock face and shuffling them up. When you felt high enough, you hauled yourself onto it. You really didn’t have the upper body strength for this. You looked for Gaster, curious as to how he would get up here. Sure enough, he was climbing up after you. If you could even call it climbing. His strange, amorphous body was simply somehow... clinging to the rock, pulling him up. Definitely one of the weirdest things you’d ever seen.

You looked up, noting with relief that you were only about a metre and a half from the top. Walking to the edge of the platform you were on, you reached for another one just above you and dragged yourself up. At this point, your arms were burning with exertion, and you were sweating profusely. You must have looked like a complete wreck. You unzipped your backpack and yanked your water bottle out, taking a long, much-needed drink. Again, you turned your head to look at Gaster. He was standing beside you, as predicted, and didn’t even look like he was breaking a sweat. _Could he even sweat?_ Before you could turn away, he waved a hand at you to hold your attention and began to write in the notebook.

**Are you alright? Hotland’s climate is far from optimal for humans, and this strenuous physical activity seems to be taking a toll on you.**

You were a little embarrassed that the fact that you were struggling was so obvious, especially given that neither the climate nor the climbing seemed to be affecting him. “I’m fine – we’re pretty close to the top. I just want to get out of Hotland. Like you said, this climate really isn’t for me.” You laughed, trying to brush off his concern, and returning your water bottle to your bag. He was still watching you, though, his mouth downturned with what looked like worry.

**I realise we are close to the top and I should have offered sooner, but I could lift you to the top so that you do not hurt yourself.**

Any other time, you would have refused out of sheer pride. But as it was, your muscles were trembling and you had a feeling your arms would give out trying to pull yourself again. You pushed aside your pride and spoke, “Actually... I would really appreciate that.” Gaster nodded, as his expression shifted from worry to relief. He turned to the wall and did his strange ‘climbing’ thing until he reached the top.

He then began reaching down. His ‘arms’ seemed to stretch beyond what they should have been able to (you figured it was yet another feature of his odd, shifting figure) until his pale hands stopped, outstretched towards yours. You hesitated for a second, before gingerly placing your hands in his much larger ones. Immediately, you noticed that his hands didn’t feel _quite_ solid (they didn’t look quite solid either). They were cool to the touch and felt like what you could only describe as thick fog. To be honest, you half expected that your hands would just slip through his at some point. But you didn’t have time to question this as he curled his fingers around yours, before beginning to lift you up.

To your profound relief, your hands didn’t simply fall through his. When you were at the top, you planted your feet firmly on the scorched ground, and the tension melted from your body. Gaster slowly released your hands once he was sure you were steady. You looked up at him and smiled gratefully. “Thanks. Let’s get out of this damn heat now!” He scribbled something in the notebook in reply.

**Agreed. Will we go to Waterfall now? Do you know the way there?**

“Yep, next stop: Waterfall.” You declared. “I know it’s West of here, but... the maps I have aren’t particularly detailed. Apparently, mapping just wasn’t a thing in the Underground.” You paused, before sheepishly continuing, “I was kind of just going to rely on trial-and-error, in terms of finding my way there.”

**Yes, it is true that maps were not commonly made here. There was no need for them. The Underground is a relatively small place and most monsters merely knew their way around.  
** **If you would like, I can direct us to Waterfall.**

Gaster watched you, awaiting your response. You may have been a little hasty in coming to the Underground today, rather than waiting until tomorrow and having Alphys as a guide. But by some turn of luck, you’d stumbled upon Gaster. You grinned at him.

“Lead the way.”

**Notes for the Chapter:**

> Aaaand that's chapter two! Hope you enjoyed it. 
> 
> Let me know what you thought!
> 
> (I'll probably be updating twice a week for the next few weeks, so you guys can expect an update in the next 3-4 days.)


	3. Waterfall

**Notes for the Chapter:**

> Hey everyone! 
> 
> Here's chapter 3 :D Hope you all enjoy it. 
> 
> As always, let me know what you think!
> 
> Tumblr (to talk to me, ask me questions, all that good stuff): https://dimetrodonao3.tumblr.com/

You’d been walking through Hotland for almost 30 minutes, when you began to seriously regret not bringing more water. It was less unbearable now that you weren’t standing directly above a sea of lava, but fire still pervaded your very bones, and the hot, dry wind bit into your skin.

Gaster was walking – _gliding?_ – beside you and had been directing you around the perimeter of the Core and through Hotland. You were definitely glad he was here with you; as it turned out, the route to Waterfall was riddled with maze-like paths, and insane traps and puzzles. Honestly, you were pretty miffed that none of this was on any of the maps you’d seen. You would have had to turn back a while ago had Gaster not been with you.

Speaking of Gaster; he really did know his way around Hotland. He knew how to navigate all the puzzles you encountered, and he knew all the shortcuts that would get you to Waterfall. You wondered if all of this was common knowledge to all monsters, or if Gaster specifically knew this area particularly well. You kept your thoughts to yourself, however, as you continued your trek.

An uncomfortably rickety, wooden bridge stretched out before you. The fact that it was wooden and rickety wouldn’t have been such a problem, had the bridge not been for the express purpose of crossing a deep pit of scalding lava. Gaster stopped in front of it and gestured for you to cross. You stared at him for a good few seconds, wondering if he was serious. “This... looks like a bad idea. Are you sure this bridge is safe?” You voiced your concern. He smiled at you reassuringly, before taking to the notebook.

**Although it looks unstable, this bridge is reinforced with magic, and has stood for as long as I can remember.**

_Of course._ Monsters have magic. You feel a little stupid now. “Ah, ok. Sorry, I’m just not really... used to magic.” You smile at him, before stepping out onto the bridge.

To be fair, you really weren’t used to magic. Yes, it had been four years since monsters had come to the surface, but you didn’t personally know that many. Besides Alphys (and, you supposed, her girlfriend Undyne), you hadn’t really had the chance to meet or get to know any. Despite the advances made, society was still quite segregated – many schools and universities didn’t accept monsters as students, many human landlords refused to rent to them, and lots of human employers wouldn’t hire them.

Because of this, many cities (including the one you currently lived in) had a ‘human side’ and a ‘monster side’ – and people didn’t tend to stray too far from where they were surrounded by others of their ‘kind’. It was terrible, you knew – but what could you, just one person, do?

You were pulled from your thoughts as you took the last step off the bridge and onto solid ground. At first you thought it might have been your hopeful imagination, but as you continued walking west, you noticed the temperature steadily dropping, the sweltering heat giving way to gentle warmth. You figured you must be near Waterfall. You turned to face Gaster, “We’re almost there, right? I can feel it getting cooler!” you beamed. He looked amused at your enthusiasm, and nodded, gesturing to a point ahead.

You followed his line of vision to see a rocky wall ahead, with a sort-of doorway made of darker, blue-grey stone. You picked up your pace, eager to get out of Hotland and see Waterfall for the first time.

The moment you stepped through the doorway, you were met with a gust of cool air, and you let out a sigh of relief. You were now in a darker cave made of the same blue-grey stone. A huff left your mouth at the enormous, obnoxious ‘WELCOME TO HOTLAND’ sign that made up the right-hand wall of the cave. “No, thank you” you pointedly rolled your eyes at it. Gaster huffed lightly in agreement.

You both moved onwards – there was nothing to really sample here, as everything was rock. You walked together in silence for a bit, absorbing the much more pleasant, cool environment. You crossed several wooden bridges over dark gaping chasms of indeterminate depth, your attention divided between the stalactites hanging like icicles from the ceiling, and the stalagmites rising like jagged spines from the inky blackness.

Gaster looked to be in awe as much as you were. His eyes seemed to be drinking in the scenery, absorbing absolutely everything he could. _Had he never been here before?_ No – he had directed you here. Plus, hadn’t he said that monsters knew the whole Underground because of how small it was? Maybe he just hadn’t been here in a while.

All trains of thought fled your mind, however, as you turned the corner to see something that made you stop dead in your tracks. A sea of flowers that were almost as tall as you were, each emitting bright blue light. Even stranger; the flowers seemed to be... _whispering?_ All in different voices, speaking different words. It was incredibly eerie, but you were fascinated. You felt a soft tap on your shoulder. You turned to see Gaster, who again, looked just as amazed as you surely did. He held up the words he had written in the notebook.

**They are called Echo Flowers and can be found throughout Waterfall. They are known for repeating the last thing they heard.**

“That’s... amazing! I – we don’t have anything like this on the surface.” You stumbled over your words – you were too incredulous to think clearly. “I need a sample.” You retrieved your sampling kit from your backpack and pulled out a new razor blade. You were somewhat nervous approaching a flower – you knew, logically that it was just a plant, but its imposing height, the eerie blue glow and the whispers emitting from it made some small part of your brain think otherwise.

You carefully sliced a paper-thin piece of stem from the flower, placing it in a sample jar. You did the same to a petal. You looked to the ground, prepared to take a soil sample, but to your astonishment, there was no soil. The flowers’ ice blue roots simply snaked around the rock. You wondered how on Earth the Echo Flowers got their nutrients. You took a root sample as well and took some pictures of the area and the flowers themselves before turning to look for Gaster.

He looked absolutely enthralled. He was standing amongst the flowers, head bent down to listen to what they were saying. The expression he wore was one you could only describe as pure joy. You couldn’t help but grin at the incongruous picture before you – this large, dark, terrifying-looking monster... smiling at flowers. It was kind of cute.

You decided not to disturb him – he looked like he was enjoying himself. Instead, you spent a few more minutes listening to the Echo Flowers yourself. You even said ‘hello’ to one, and were thoroughly creeped out when it had parroted the word back to you in your own voice. You would _have_ to tell your human friends about this. More than anything, you wanted to know how exactly the flowers worked, but you strongly suspected you would be met with the same answer that applied to so many aspects of the monster world – magic.

You felt a cold hand brush your shoulder briefly to get your attention. You twisted around to be met with the sight of Gaster’s awestruck smile. He had written something in the notebook.

**I cannot thank you enough for offering to bring me here. It has been so long since I have been able to leave that spot in Hotland. Truly, I am so grateful.**

You were struck with sadness at his words – just how long had he been stuck in Hotland? “Hey, I should be thanking you for showing me how to get here in the first place. I never would have made it here without you. But…” You considered your next words carefully, “exactly how long were you stuck in Hotland?” He looked down for a second, before writing his answer in the notebook.

**I am not sure of the exact length of time that transpired, but I suspect I was there for several years.**

_Several years?_ You were shocked into silence. You knew he had to have been in the Underground for at least four years to have never seen an adult human, but he had been in the exact same _place_ in Hotland for all of that time? Maybe even longer? Your heart ached as everything was put into context. No wonder he was so wondrous and ecstatic about seeing all these places again.

“Shit, I’m… I’m so sorry,” you stuttered, completely unsure of what you should say in this situation. “I had no idea. I must seem like such an asshole – I mean I’ve just been dragging you along while I do work, I haven’t even… I’ve barely had a proper conversation with you. I didn’t even ask if there was anywhere _you_ wanted to go!” You were rambling again. “ _Is_ there anywhere you want to go? Do you have like… family, or friends, or anyone I can help you find?” He stopped you there, wearing a pained expression at the mention of friends or family. He scribbled something down before showing it to you.

**No, you have no reason to be sorry. I am in this position purely of my own doing. It is no one’s fault but mine. I am very much enjoying your company, however, and I am perfectly happy to watch you work. As for friends or family – I do not have any. Not anymore.**

“… Ok. I’m sorry to hear that.” You decided to stop pressing, even though you had so many more questions. You didn’t want to upset him any more by bringing up bad memories. “… Shall we keep moving on, then?” You questioned, hoping to alleviate the dark mood that had settled. Gaster seemed to want to do the same, because he smiled at you gratefully, and nodded. You kept walking on, in companionable silence.

* * *

 

Within about fifteen minutes of trekking through more rooms of the massive cave system, you found yourself in what was easily one of the most beautiful places you’d ever seen.

It was an expansive part of the cave, with the highest ceilings you’d seen, where the dark mossy floor was disrupted by several pools and channels. The water that filled them had an electric blue sheen, that you suspected was caused by bioluminescent algae. You could have jumped for joy. There was so much more to learn from a place like this than bloody Hotland.

“This is amazing!” You voiced your thoughts, spinning around to face Gaster. “I’m gonna take _so_ many samples.” He grins at your enthusiasm, making a sweeping gesture around the cave as if to say ‘go nuts’. Although he would probably say something more eloquent than that.

You start with the dark moss clinging to the rock beneath your feet, using your razor blade to prise it off, before moving on to the water. _Water!_ Despite the cooler climate here, you were still feeling pretty dehydrated from your escapade in Hotland. You hesitated, however. “Hey, Gaster?” You asked, turning to face the former-scientist, who was currently gazing down into another pool. He glanced up to meet your eyes. “Is this water drinkable?” He nodded, before turning to the notebook to elaborate.

**It is perfectly safe. Although you may want to avoid the algae on top.**

Was that his attempt at… a joke? You glanced up at his expression. Sure enough, he was grinning back at you. You snorted. “Thanks, Captain Obvious,” you grinned back. You pulled your bottle out of the bag, unscrewed the lid, and stuck it in the water, well below the algae. When it was full, you covered the opening with your hand and lifted it out of the water, grimacing at the sheen of slimy blue algae that now coated your hand. You shook it off, before gulping down some much-needed water. After you’d refilled the bottle again, you put it back in your bag, and took a couple of algae samples. You then grabbed your water testing kit and noted a few key observations about the water quality. You also took a couple of water samples so you could analyse them in greater detail back at your lab.

Glancing around the cave, you figured that that was all the samples you would need from this room. Now it was time to just enjoy your surroundings. You pushed yourself to your feet, brushing your palms off on your jeans. Gaster had moved, and was now seated beside a larger channel, lightly running a hand through the water. You approached him from the side, and sat down next to him, crossing your legs. It was odd – normally, you would have preferred to be alone while you were gathering data for your research. People’s presence tended to annoy you when you were working. But you were really enjoying Gaster’s company (and the feeling seemed to be mutual), and he had genuinely helped you a lot today. You’d thought it several times already, but you were _really_ glad you’d found him.

“I was wondering...” you began, getting his attention, “the different ‘regions’ down here would have had completely different types of monsters in them, right?” You’re curious, because on one hand, you thought that with technology and magic monsters could have surpassed any natural limitations they might have had with regard to climate (just like humans had). But on the other hand, there was so much physical variety in monsters, and a lot of them seemed highly adapted to specific environments – perhaps monsters _did_ only live in environments they were adapted to. Or maybe it was a combination of both.

Gaster seemed to follow your train of thought, because he launched into writing a lengthy explanation into the notebook. You should really try to start learning some sign language before you came down next time.

**Yes, you are correct. Though we could use our technology, and our magic to an extent, to enable ourselves to live in environments that we were not adapted to, many (but not all) monsters understandably chose to remain in the environments that suited their physiology best.**  
**For example, many reptilian monsters chose to live in Hotland, many amphibious and fish-like monsters lived here in Waterfall, and most mammalian monsters lived either here or in Snowdin.  
** **The monsters who chose to live in environments that they were not necessarily suited to used things such as air conditioning and humidifiers to alter their homes and make their lives more comfortable.**

You paused, wondering idly if Alphys had lived in Hotland. And if perhaps Undyne lived somewhere around here. Maybe you’d ask when you got back. “Makes sense,” you responded to Gaster thoughtfully, “Thanks.” You hesitated for a second, before letting your curiosity get the better of you. “Did you live in Hotland? Before you were stuck there, I mean?” His eyes flicked to the floor for a moment, betraying his shame, before writing in the notebook.

**No, I did not live in Hotland, but I worked there. It was where my lab was located. I lived in Snowdin.**

“Snowdin, huh?” you nodded to yourself absently, “I’m pretty much done here – if I see anything else I want to sample on the way, I’ll do that, but why don’t we head over to Snowdin now? You must miss it.” Gaster gave you a wistful smile, nodding once in response.

“Alright. Snowdin it is, then.”

**Notes for the Chapter:**

> Next up: Snowdin! 
> 
> Hope you enjoyed this chapter. The next one will be up in 3-4 days, as usual :D


	4. Snowdin

**Notes for the Chapter:**

> Hey everyone!
> 
> Thanks so much for all your comments and kudos :D I really appreciate all the encouragement so far!
> 
> Here's chapter 4!
> 
> Tumblr (to talk to me, ask me questions, all that good stuff): https://dimetrodonao3.tumblr.com/

You and Gaster were steadily approaching an immense dark wall of roaring water, which crashed down into the river metres below you. You figured that this must be the titular waterfall. You had made it here after a trek through the cave system, helpfully guided by Gaster (even though Waterfall was _nothing_ like the intense hostility of Hotland with all its traps and puzzles). On the way, you had taken some quick samples – in a section with a soil-covered floor, you had sampled some luminescent blue mushrooms, some intimidatingly tall grass, and some of the soil itself. You had also taken samples of these lily pad-like flowers, which were apparently called ‘Bridge Seeds’, a couple of water samples, and some samples of strange-looking reed plants which Gaster informed you were called ‘Water Sausages’. Monsters seemed to be quite matter-of-fact when it came to naming things.

Nevertheless, you were here now. The two of you walked beside each other, across the pathway underneath the crashing waterfall. For a few seconds, your ears were filled with the roar of the rushing water (and, to a lesser extent, the constant static hum that seemed to accompany Gaster). And then, you were out on the other side. You instinctively squinted at the bright light that met your eyes.

When your eyes adjusted, you realised that the light came from a narrow opening at what looked to be the end of the cave system. You turned your head to look at Gaster, who was shielding his eyes from the light with his hand as he became accustomed to the brightness. “This must be the end of Waterfall, right?” you questioned. Gaster lowered his hand, before nodding in affirmation. It may have been your imagination, but he almost seemed... anxious? Nervous? It made sense, of course – he was coming back to the place he had lived for the first time in god knows how long.

Keeping that in mind, you proceeded through the exit of the cave and are instantly met with snowflakes, landing on your hair, your shoulders, and, annoyingly, your glasses. It struck you in that moment just _how_ _small_ the Underground really was. You figured you could walk across the entire thing from one side to another in around one and a half, maybe two hours. That realisation was totally incomprehensible when you considered just _how many_ monsters had lived down there. They must have been packed like sardines. The thought upset you – it was wholly unfair that monsters had escaped the Underground, only to be confined again on the Surface in a completely different way. 

You trudged through the snow, sobered by your thoughts. You spun around at the feeling of a large hand on your forearm. Gaster started slightly at your reaction. “Sorry,” you breathed, “I was a little out of it for a second there.” He pointed at something he’d written in the notebook.

**I do not wish to presume, but did you want to sample the trees here?**

You blinked. You lifted your head and looked at your surroundings. The path behind and ahead of you was covered in a thick layer of crisp snow, and to both your left and right were densely packed forests of what looked like pine trees. You smiled gratefully at Gaster. “Yeah, that’s a good idea. Sorry, I really was completely lost in my head for a bit. Thanks for reminding me.” He brushed off your apology with a small wave of his hand. You jogged over to the trees and began carefully slicing off pieces of bark and leaves, placing them gently into sampling jars. You also snapped some pictures for later reference. When you were done, you returned to Gaster, who currently had a hand outstretched, collecting snowflakes as they fell. If you were to guess, you would say he looked nostalgic.

When you approached, he drew his hand back and fell into step with you as you proceeded along the path. Now, you thought as a gust of freezing wind whistled past, you were starting to feel glad that you had worn a sweater. You watched the trees as you continued walking – and suddenly something occurred to you. There was no sunlight down here. How were any of these plants alive? You cast your eyes up to the high ceiling in search of the light source, and were immediately astonished at what you saw. The high roof of the cave was not rock; it was made of a strange, jagged, mirror-like material that both reflected and refracted the little light that came from the yellowish bioluminescent moss that grew up there. It was... pretty amazing.

The source of the snow, however, was a little more elusive to you. There weren’t even any clouds or anything – the snow just seemed to... materialise at the top of the cave and fall down. Gaster must have noticed your puzzled expression targeted at the ceiling, because he was writing something in the notebook for you.

**The snow is magical; it recycles itself. The layer at the bottom continuously disappears and is relocated to the roof, where it falls down again.**

You couldn’t help but laugh. “Magic. Of course! That seems to be the answer to just about everything when it comes to monsters.” You shook your head, grinning. He seemed to understand your plight, because he laughed silently as you kept walking on.

It wasn’t long before you reached the town. It looked like it must have been cheerful and homely, once upon a time, but now it was eerily silent and empty. You first passed a large, wooden house with a matching shed beside it. Gaster wore an unreadable expression as you both approached it. Its roof and door were lined with Christmas lights, which still glittered red and green. Curiously, you noticed a skull-and-crossbones flag sticking out of the side of the roof. Some of the lights were also on inside. “How is there still power down here?” you asked Gaster, incredulous. You had heard about the Core, and how it had provided clean energy to the Underground, but surely it wasn’t still running... was it?

**I do not believe the Core was ever shut down. It is likely still supplying energy. I was not sure whether it would be able to be completely self-sufficient – able to run without maintenance or extra cooling – but it seems to be holding up well.**

Gaster looked almost... proud, at the revelation that the Core was still running. And the way he spoke about it seemed to you like he had been personally involved with running or maintaining the Core. He did say that he used to be a physicist. “Wow,” you were genuinely impressed that the Core was working on its own, “that’s amazing. Humans would _die_ for that kind of technology. We’re kind of in the middle of an energy crisis.” Gaster looked intrigued, scribbling something down in the notebook.

**It may be difficult, but I have no doubt that a version of the Core could be replicated on the Surface. Has no one attempted to do that, yet?**

Your features formed a puzzled expression. “I don’t know. I assumed that it was impossible – because surely someone would have tried?” You honestly weren’t sure. Well, that was something to store away in your mind for later. You’d have to do some research, ask Alphys maybe. Gaster seemed to be mulling over your response – you could almost _feel_ his mind whirring.

His eyes were still narrowed in thought as you kept moving through the town. You passed the ‘libarby’ – _library?_ – and came to a fork in the path. Straight ahead seemed to be the way to the other end of Snowdin, but there was a path that led right, to a suburban area. Before you could make a decision, Gaster was heading right. He looked as if he was almost in a trance. _Maybe his house is somewhere there._ You weren’t sure what would happen if Gaster got too far from the grey thing in your bag, but you didn’t want to find out. You jogged to catch up with him a little.

He had stopped dead in the middle of a clearing, staring at an empty lot to your right. His features formed a mask of utter devastation. You weren’t sure if you should ask him what was wrong and try to console him, or if you should leave be, in case he didn’t want to be disturbed. Eventually, you plucked up the courage to approach him. “Hey,” you began softly, getting his attention, “is... is everything ok?” He kept his eyes on the empty space for a moment, before writing in the notebook.

**I used to live here. My house used to be here. Now it is just... gone.**

You didn’t know what to say to that. You couldn’t even imagine going home one day, only to find your house, all your belongings, _everything_ – just gone.

**It feels as if... as if the world simply moved on without me. As if everybody I cared about forgot about me. As if I never existed.**

You were silent for a minute. _What could you say to that?_ “I’m so sorry.” Your words felt wholly insufficient. You hesitated for a second, before placing a hand on his arm. It was cool to the touch and felt like what you could only describe as kind-of solid water. He seemed a little stunned at first, but accepted your touch. You stood beside him in quiet sympathy and solidarity. You weren’t quite sure how long you stood there, but eventually, Gaster let out a slow breath, and wrote something down.

**We should keep moving if you want to see the rest of Snowdin today and make it back to the Surface at a reasonable time.**

You nodded and took your hand off of him. He turned away from the spot where his home used to be, and you both walked back to the main area of the town. Even though he had physically moved away from his old home, you could sense that he was still ruminating on it. On the fact that the world had gone on without him, and that it barely seemed to notice his absence. You decided to let him be – he seemed to want you to forget about it.

So you turned your attention back to the town. You were passing what looked to be a bar, or a restaurant with a large painted sign across the top which read ‘GRILLBY’S’. For some reason, that name sounded familiar to you. Wasn’t there a bar on the monster side of town with that name? You’d never been (you would have felt too out of place), but you had walked past it a couple of times. It must have been run by the same person who ran this one. You also passed a Christmas tree (which, like the house you had seen before, was strung with Christmas lights which still shone with colours) and an inn, and then you were out of the small town.

Unfortunately, there wasn’t that much to sample in Snowdin. This became apparent to you as you continued walking west, through the thick, pristine snow. The whole area was populated only with dense forests of the same pine trees you had already sampled. Nevertheless, you persisted onwards. Gaster was still silent, deep in thought beside you.

Soon enough, you entered an area where the pine trees dropped away, and were replaced by thin, dark, towering trees which brushed the ceiling of the cave. “I’m just going to sample these quickly,” you murmured, before slicing off some pieces of bark. The leaves were far too high for you to reach, but there were a few that had been shed onto the floor. They were less ideal than the ones still attached to the trees, but they would have to do. You also took a couple of pictures of the area.

When you were done, you flashed a quick smile of thanks towards Gaster for waiting (not that he could have moved away from the grey thing in your bag, but still), before proceeding down the icy path. It wasn’t much longer before you reached a large purplish stone structure with an archway at the entrance, which, unlike the cave system, looked to be deliberately constructed, rather than naturally occurring. You knew from the maps you had studied that this must have been the Ruins.

You had thought about going there but had ultimately decided that there wouldn’t be anything useful to sample inside. Besides, even if there were, it wouldn’t be conducive to your research. To your understanding, no one had lived in the Ruins, so there was no reason to study it as an environment which would have impacted the evolutionary progress of monsters. You might go at some point in the future, just to check it out and see what it was like, but you wanted to get back home for dinner and you had a feeling you’d been here too long. You checked the time on your phone – 3:14. Not too bad. It would take you about an hour and a half to get back to the Underground’s entrance, and another hour to drive home. If you left now, you would be making good time.

But – there was still the conundrum of Gaster. He could only move around with you if you had the grey thing. Otherwise, he was essentially stuck in one spot. _Like he had been for at least four years._ You decided to bring it up to him and let him decide what he wanted to do. “I think I’ve got all the samples I need for today, so... I should probably be heading off. But I would feel awful just leaving you here, even if I’m coming back in another week or so. So, what do _you_ want to do? You could stay here in Snowdin, or anywhere else in the Underground – you could even come to the Surface with me! That way you wouldn’t be stuck in one spot, and you wouldn’t have to be alone...” you trailed off, consciously cutting off your own rambling. Gaster offered a small smile, before writing down a response.

**I would rather not stay in Snowdin; I have too many memories caught up here that I would rather not re-live. As much as I appreciate your offer to take me to the Surface with you, I cannot accept it. Again, there are many ~~people~~ things there that I cannot face yet. I would be grateful if you simply left me in Waterfall, on your way back, in the area where the Echo Flowers were. **

You wanted desperately to know what had happened to land Gaster in this position. Why he carried such an air of melancholy about him. What he had done to make himself think that he deserved this. But you knew if you asked now, you wouldn’t get any answers, and would risk destroying the fragile, tentative trust you had developed. So you just nodded, and replied “Of course I’ll take you back to Waterfall. Let’s get going.” He seemed to appreciate your lack of questioning, because he smiled at you with gratitude before you began the trek back to Waterfall.

* * *

About 45 minutes had passed by the time you reached the Echo Flower area in Waterfall again. The room swelled with the flowers’ whispers, forming a strange chorus amidst the eerie silence of the cave system. The electric blue glow that was emitted by the flowers enveloped the whole room, making it feel dreamlike and surreal to you.

You stopped in the middle of the sea of flowers. “Well,” you began, with an air of finality, “Here we are.” You hesitated, but then spoke again. “Listen – are you sure you want me to leave you here? Are you sure you don’t want to come to the Surface?” Gaster smiled ruefully, before responding through the notebook.

**I am sure. You plan on coming back to the Underground for further research, do you not?**

He waited for your confirmation, which you gave with a nod, before continuing.

**Then perhaps one day, when I am ready, I will come up with you.**

You breathed out through your nose, upset and mildly frustrated that you couldn’t convince him to come with you. You just felt so bad about having to leave him here. But what could you do? You noticed Gaster taking to the notebook once more as you unzipped your bag to retrieve the grey object.

You gently grasped the grey thing, feeling its smooth, rippling surface beneath your fingers. You lifted it from your bag and held it delicately in both hands, relishing in its coldness on your palms. Gaster turned the notebook to you.

**I cannot thank you enough for all you have done for me today. Because of you, I have been able to move around the Underground again and speak to another person for the first time in years. So, thank you, Y/N.**

You gave him a half-smile, touched at his gratitude, but sad that you had to leave him here. “Don’t mention it. Thank _you_ for coming with me and guiding me through this place! I would never have made it any further than Hotland on my own.” He nodded, before seemingly realising something and writing in the notebook.

**Will you be alright traversing Hotland on your own? Do you remember the path we took, and the solutions to the puzzles?**

You weren’t sure you did. Not completely, anyway. But seeing the concerned look on his face, you decided to lie for his sake – you really didn’t want him to have to spend another week or so in Hotland because you couldn’t remember some directions. “Yeah, I remember. I’ll be fine. I’ll be back in about a week, once I’ve had a look at the initial samples I’ve got. So, I guess... I’ll see you then.” Gaster wrote his response down, and turned the notebook to show you.

**Alright. I will see you in a week. Goodbye, Y/N.**

You gave him a small wave and a grin, before gently placing the grey thing on the ground, spinning on your heel, and beginning your walk back to the Surface.  

**Notes for the Chapter:**

> That's chapter 4! Hope you guys enjoyed it. 
> 
> Let me know what you thought!
> 
> Also - I've decided I'll be posting every Tuesday and Saturday (Australian time - so if you're in the US it'll be Monday and Friday).


	5. Home Again

**Notes for the Chapter:**

> Hi everyone! 
> 
> Here's chapter 5 :D 
> 
> We've got a new character introduced in this one, and our reader uncovers more strangeness around Gaster. 
> 
> Hope you all enjoy it.
> 
> Tumblr (to talk to me, ask me questions, all that good stuff): https://dimetrodonao3.tumblr.com/

It took you longer than you had originally thought to walk back through the rest of Waterfall, and through Hotland and the following castle area, because you had taken a couple of wrong turns and had to backtrack a little. But eventually, you found yourself on the steep, rocky upwards climb through the cave up to the Surface. 

Your face broke into a beaming smile as a pinprick of natural light appeared ahead. Suddenly re-energised, you picked up your pace, and emerged from the darkness of the cave. You felt the rush of fresh air, and the late afternoon sunlight on your skin. You couldn’t even imagine how it must have felt for monsters to reach this point after spending their entire lives Underground.

A sigh escaped your mouth as you saw your car, parked a few metres away, which had been sitting in the scorching sunlight all day. No doubt it would feel like an oven inside. It hadn’t even occurred to you in your excitement this morning to try parking in the shade. Deciding that there was no point in delaying the inevitable, you unlocked the car, opened the door, and climbed inside. As predicted, it was unbearable inside – you couldn’t even touch the steering wheel without burning your hands.

You immediately started the engine to get the air conditioning going, and when it was cooler, you began the long trip back home.

* * *

 

When you got back to your apartment, you were starving. You had eaten an apple this morning on the way to uni, and a couple of muesli bars as you were walking around the Underground with Gaster, but you hadn’t really had a substantial meal all day. You had planned on buying lunch at the university, but of course you hadn’t considered your impromptu journey to the Underground. The thought of having to cook when you were so exhausted was draining, but you were so damn _hungry_.

You pulled the fridge door open, pursing your lips at its sparse contents. You supposed you could make a chicken stir fry with some of the vegetables you had. Your mind began to wander as you organised the ingredients and started preparing your meal. You couldn’t help but wonder what Gaster was doing right now. Of course, you knew he would still be in the Echo Flower field – he couldn’t have moved from there. Was he still listening to the Echo Flowers? Well, that was all he really _could_ do, wasn’t it? Your heart sank when you really thought about that – he would be sitting in the field, listening to the flowers for a week straight before you came back down for him.

You switched off the stove when you decided the food looked cooked and spooned it onto a plate. Barely waiting for the stir fry to cool down, you shovelled it into your mouth. You couldn’t remember the last time you had been so desperate to eat a meal. As soon as you were finished, you got up to take a shower, peeling your sweater and jeans off (which were both filthy at this point). The shower was long and relaxing, and you relished every minute of it. Once you were satisfied that the sweat and grime had been washed off you completely, you reluctantly turned the water off and stepped out of the shower, drying yourself and changing into the pair of shorts and t-shirt you often slept in.

Cursing softly, you realised you had forgotten to unpack your samples. It was too late to go to the lab now, so you decided you would keep them in your fridge overnight and take them to the lab for analysis with you tomorrow morning. Padding softly into your living room, you curled up in your large armchair beside the fish tank which housed your little catfish. For a few minutes straight, you watched May with fondness as she snuffled around on the bottom of the tank. This was one of your favourite pastimes – you found it so relaxing, just watching May living her life without a care in the world.

Again, your mind began to drift to Gaster. You _really_ should try to learn some sign language before you went to the Underground again in a week. It was kind of cumbersome trying to communicate via notebook – not to mention, you felt bad that you couldn’t understand him when he spoke in the way that was likely the easiest for him. But you were too tired tonight. Maybe you would start learning tomorrow after work. 

You shifted in your armchair, diverting your eyes from May to the TV on the wall in front of you. Right now, you felt like the only thing you could do was watch some mindless TV. So that’s exactly what you did – you pulled up Netflix and started playing your favourite trashy show, ready to switch your brain off for a while. Before you could really get into it, though, you heard your phone vibrating on the dinner table. Your head lolled back in frustration, but you ultimately switched the TV off and heaved yourself up to go answer it. You were glad that you did when you saw the caller ID – it was Quinn!

Quinn had been your friend since the last couple of years of high school and was one of the only friends you had stayed in contact with since then. She was like the yin to your yang – while you were kind of shy, introverted, and awkward, Quinn was bubbly and outgoing. She had a magnetic personality – one of those people that you just couldn’t help but like. She always liked to tease that she ‘adopted’ introverts like you and befriended them. It was true, in a sense. Anyway, you hadn’t spoken to her in a while, so you were ecstatic that she was calling.

“Hey! How’re you doing?” you grinned as you answered the phone.

“Y/N, hi!” you heard Quinn’s cheerful voice on the other end, which instantly perked your mood. “I’m doing great. I got to do a dolphin autopsy yesterday, so... that was a new experience.” She chuckled. Quinn was a vet – not the kind that dealt with neighbourhood cats and dogs, but the kind that worked with exotic animals at a zoo.

“Fun.” you responded, “still enjoying your job, though? I know you were a little unsure about it at first...” you trailed off.

“Loving it.” Quinn replied with no hesitation. “Right now, this is something I can see myself doing for the rest of my life, to be honest.” You smiled, glad that your friend was happy.

Before you could say something back, Quinn continued, rapidly firing off several questions, “How’s your life, though? Anything interesting to report? Made any more progress on your research? Any new friends? You know you really need to get out there and talk to more people.” It was true – since you had moved away from your home and your friends to Ebott for your research, you’d had trouble getting to know more people. Alphys was one of your only friends in Ebott, among a couple of other co-workers.

You laughed at Quinn and began answering her questions one-by-one. “Life’s great! And actually – you called at exactly the right time – _boy_ do I have something to report. My application for permission to enter the Underground; it was accepted today! Quinn, I actually went to the Underground today!” you paused, allowing your friend to gasp and cheer in excitement.

“Oh my god, Y/N, that’s _huge_!” she exclaimed. “Congratulations! So, how was it? Did you make any breakthroughs? Learn anything new? Did you take pictures?”

“Thanks, Quinn,” you responded. “It was incredible. Today was mostly a lot of sample-taking – I haven’t actually analysed anything yet. That all comes tomorrow. But the Underground... it’s not like anything I’ve ever seen up here. It’s so completely unique and diverse and... You really have to see it to believe it. I did take lots of pictures, though! I can send some to you later.” You paused your excitement-fuelled rambling, wondering whether you should tell her about Gaster.

Part of you wondered if he’d mind you telling others about him – not that he’d said anything to indicate that, but you kind of felt like he should be... secret. Private. But you hushed that part of yourself, telling yourself silently that you were being ridiculous. Besides, Quinn _had_ asked if you had made any new friends. You weren’t sure you could call Gaster a friend just yet, but you felt like maybe you could in the future. You had _talked_ to him, after all. And he seemed like a sweet person, overall – even if he obviously had some unresolved issues, and a mysterious past.

“Actually, I met someone down there,” you began slowly.

“Wait, what? In the Underground? I thought there was no one left down there.” Quinn’s tone betrayed her confusion.

“Yeah, so did I. But I found this guy down there. A monster, obviously. He said he wasn’t ready to come to the surface. But he helped me find my way through the Underground – seriously, there is so much crazy shit down there that isn’t on the maps.” You shook your head. “He was with me the whole day. He said his name was W.D. Gaster.” You paused for a second. What did the W.D. stand for? It hadn’t occurred to you to ask at the time – you had just taken to calling him ‘Gaster’. But was that his surname? You would have to ask when you went back down.

“That’s... strange,” Quinn replied, thoughtful. “But he helped you. Anyway, good for you! Talking to people, making new friends. Seriously, you do need more friends in Ebott. You know, people to spend your free time with! Have fun with!” You hummed, deciding not to tell her about Gaster’s strange predicament of not being able to move away from the mysterious grey object. “Anyway,” she said, “I’ve gotta go. I have like a million things to do tomorrow, so I really need to get my shit together. Don’t forget to send me those pictures of the Underground!”

You laughed at her, “Ok, ok. See you, Quinn.”

“See you, Y/N!” she chirped, before hanging up.

You felt a lot less tired after your conversation. Maybe Quinn was right; you needed more of this. More light, carefree moments with friends. More opportunities to share what was going on in your life with people who actually cared. You put the phone on the side table where May’s tank rested and turned the TV back on. Time for a perfect quiet evening of laziness and crappy shows.

* * *

Your eyes snapped open at the shrill blaring of your phone’s alarm. After yesterday morning’s rushed panic, you had decided you weren’t making the mistake of not setting an alarm again. You groaned, and fumbled for your phone, switching the alarm off and swinging your legs over the edge of the bed. _8:30_. You had a comfortable one hour to get ready and get to work. You planted your feet on the floor and got up to start your morning routine.

It was 9:02 by the time you had gotten dressed, eaten a quick breakfast, packed some lunch, brushed your teeth and gathered your work things, including yesterday’s samples. You were making good time. You moved to the living room and shook some food into May’s tank, watching as she emerged from her hiding spot inside the fish tank accessory log you had bought her. As you walked out of the apartment, you grabbed your lab-coat from the hook beside the door where you had left it after coming home last night.

The walk to uni was nowhere near as rushed as it had been yesterday, and it was just about time for work to start when you arrived. You buzzed yourself into your lab, slipping on your lab coat before removing the samples from your bag and arranging them on the bench space. Before you started your analysis, though, you decided to pay a quick visit to Alphys.  

You left your own lab and made the short trip down the hallway to Alphys’ lab, rapping a quick knock on her door. “C-come in!” you heard her call quietly. You pushed the door open with your hip, and smiled at the lizard monster, who was currently tinkering with a machine on her bench. You had only been into Alphys’ lab a few times – it was always packed with intricate, complex machines that she had built, half of which you had no idea what they were for. You’d made a habit of asking her about a different invention each time you visited. It was kind of a tradition, at this point.

“Hey Alphys!” you greeted, before your eyes caught a small, white machine with a glass chamber, a keypad, and a screen. It was secluded in the corner of the room, tucked behind other inventions – almost like it was being hidden. “What does this do?” you asked her, navigating your way to it. You didn’t miss Alphys’ quickly masked expression of discomfort – it occurred to you then that maybe this machine was ‘hidden’ for a reason. “Um... it’s... it’s called a soul tracker.” She mumbled, tail swishing nervously. “I don’t use it any more. It’s k-kind of an invasion of privacy...” she trailed off, before rushing to explain. “I built it in the Underground, to – to track Frisk. Y-you know, the ambassador?” you nodded – you knew about the human child who had somehow freed the monsters and become their representative, of sorts. “It... you just have to get a reading of someone’s soul, and you can... track it’s location...” she stopped for a second. “But! I haven’t used it s-since Frisk. And I don’t plan to. So...” she wringed her hands together, looking embarrassed.

You were admittedly a little unnerved that Alphys had made something like that to track a child. But she was clearly ashamed that she had made it, and clearly didn’t plan on using it in the future. So you tried to make things less awkward. “Well... It’s pretty impressive, even if it is a little... intrusive.” You cringed at yourself. “Anyway,” you turned away from the soul tracker, toeing your way back towards Alphys. “I came to tell you about yesterday!” Alphys brightened immediately, seemingly eager to hear about your trip.

“Y-yeah!” she grinned, “How was it? D-did you get all the samples you needed?”

“I did! I’m going to analyse them today!” you exclaimed, “Alphys, it was so amazing down there. So completely different than it is up here. I can’t wait to go back down.” You stopped for a second – should you tell her about Gaster? Maybe she knew who he was. Maybe she could find some way to help him. You decided to bite the bullet. “Actually, there was someone down there.” Alphys looked shocked.

“W-what?” she stuttered, “I thought everybody came to the Surface.”

“He said he wasn’t ready to come up.” You explained. “His name was W.D. Gaster – he said he was a scientist. Did – did you know him, by any chance?”

Alphys was silent for a minute. She furrowed her brow in deep thought. “Th-that name sounds... familiar...” she looked disturbed. “I... I don’t think I know him, but... For some reason, I feel like I _should_ know.” Alphys was looking more and more troubled. “It’s like... on the tip of my tongue... but...” she sighed, frustrated, “Why can’t I remember?” She looked thoroughly unsettled. You decided to just change the subject – this seemed to be upsetting her.

“Well, anyway,” you said in a chipper tone, “Just wanted to thank you for delivering the permit to me yesterday. I should really get to analysing those samples now.” Alphys snapped out of her unease. “N-no problem, Y/N. I’ll see you later!” she smiled and waved a clawed hand at you as you left her lab.

Finally, it was time to take a look at those samples!

**Notes for the Chapter:**

> Hope you guys liked chapter 5!
> 
> I know - no Gaster in this one, sadly. But don't worry, he'll be back soon!
> 
> Let me know what you guys thought about this one.


	6. Friends?

**Notes for the Chapter:**

> Hey guys!
> 
> These chapters keep getting longer and longer...
> 
> In this one, Reader gets to know some other characters, and makes some friends. Also - more strangeness around Gaster! 
> 
> Hope you like it!
> 
> Tumblr (to talk to me, ask me questions, all that good stuff): https://dimetrodonao3.tumblr.com/

You stretch your arms over your head, and glance backwards at the clock. Yep – definitely time to be heading home for the day. You got up from your stool, and started packing away your samples, your microscope, and your other equipment. As you pulled your lab coat off and went to wash your hands before leaving, the door to your lab was flung open with a bang. You started, splashing water all over yourself.

“Shit...” you murmured, before shutting the water off and turning to see who it was.

“HEY, PUNK!” yelled a raspy, feminine voice. As you suspected, Undyne – Alphys’ tall, fishy, _loud_ girlfriend – had just barged into your lab. Alphys stood outside the door, giving you a sheepish, apologetic smile. You were kind of used to Undyne’s eccentricities, as it was rare to go for a week without her visiting her girlfriend at work. Nevertheless, you were a little startled. 

“Hi, Undyne.” You replied, giving her a small wave. “Nice to see you again.” She flashed a toothy smile at you, striding into the lab to talk to you properly as Alphys followed. “So, you and Alphy are friends. Which means you and I are friends.” Undyne stated matter-of-factly.

“I... yeah?” you responded, not quite sure what she was getting it.

“And friends hang out with each other OUTSIDE work, right?” she emphasised.

“Right...” you parroted.

“So you should hang out with us! We’re goin’ to Grillby’s for dinner tomorrow with a couple friends – come with us!” she grinned, anticipating your response.

You were rendered speechless for a moment – they were... inviting you to dinner with some friends? You felt oddly touched that they would do that. That they actually wanted you around. “Yeah, of course.” You smiled appreciatively at them both. “I’d love to!”

“AWESOME!” Undyne yelled, startling you again. “Meet us there at 7 tomorrow, ok? C’mon Alphy!” she turned away, marching out of the door. Alphys scratched the back of her neck awkwardly, before attempting to explain. “U-uh... Undyne has been trying to get me to make friends at work, and... especially human friends, you know? But! D-don’t feel obligated to come, if you don’t want t-to...” she trailed off, wringing her hands together.

“No! Honestly, I’d love to come.” You reassured her quickly. She smiled, relieved, and hurried out of the lab to catch up with Undyne.

You breathed out as you realised what you’d just agreed to. This... was good, right? You were making friends. Now that you thought about it – this would be the _first_ time you’d ever gone out with other people since you’d moved here. Yes, this was definitely a good thing.

With a smile on your face, you dried your hands and began the walk home. You had gotten a lot done today. Your samples revealed that the water in Waterfall was incredibly high in nutrients – abnormally so. You supposed this explained how so many of the plants (including the Echo Flowers) there were able to grow without any soil – they got their nutrients straight from the water. The next time you went down, you would have to look around for the source of the water – try and see how it became so nutrient-rich. You had also found, to no surprise, that Hotland’s soil was almost totally devoid of nutrients. It made sense that there were no plants there, with that knowledge. But it made you wonder; aside from its scorching temperature, what was the advantage of Hotland for reptilian monsters? What was their food source? Or did they just import all their food from the other areas of the Underground? More questions you’d need to search for answers to when you were down there next. One of the more puzzling things you’d observed was that none of the trees in Snowdin, nor any of the plants in Waterfall, had any chloroplasts. Another mystery to be solved – how did Underground plants get their energy, if not by photosynthesis? 

You needed all of this information to build a bigger picture of the Underground – to understand the environment, and therefore how and why monsters evolved to be the way they are. To your understanding, monsters were far less diverse than they were now before they were forced Underground by humans, hundreds of years ago. You knew this because of historical writings and artworks. Your current line of thought was that the extreme environments of the Underground had forced monsters to adapt rapidly, to vastly different environmental conditions, resulting in the diversity that could be seen in monsters today. But before you could conclude anything, you really needed to get more information.

You pushed your glasses up as you unlocked your front door, letting yourself into your apartment. You hung up your lab coat on the hook by the door, and made a beeline for your armchair, carrying your laptop under one arm. You sat down, tucking your feet under you, eyes searching for May in the fish tank beside you. As usual, the timid catfish was relaxing inside her log. Satisfied that your companion was alright, you resolved that you needed to start learning ASL today. You wanted to have made _some_ progress by the time you saw Gaster again. Like, at least know how to recognise some basic signs – ‘yes’, ‘no’, ‘hello’, etcetera.

So you opened your laptop and pulled up YouTube, starting the search for ASL tutorials. Tonight was going to be a long night.

* * *

 

You spun in your stool at the lab restlessly. Since being invited to dinner with Alphys and Undyne and their friends yesterday, you couldn’t keep the anticipation for tonight out of your head. You were nervous and excited, and you were having trouble focussing on your work because of it. You had been doing a closer analysis of your samples and writing up all of your findings and hypotheses so far into a report. The report was pretty much finished – but it had taken you longer than it should have. The whole day, in fact. It was time for you to head home and start getting ready for tonight.

An endless stream of anxious thoughts roiled in your mind as you left your lab and started the walk home. What if Alphys and Undyne’s friends didn’t like you? What if that made Alphys and Undyne not like you? What if their friends... hated humans or something? Did they know you were human? Did they even know you were coming? _Shit_... you felt like so much could go wrong tonight. _But things could go really well, too_ , a small part of your mind reminded you as you pushed your apartment door open.

You were supposed to meet them at Grillby’s at 7. A quick visit to Google Maps told you that it would take around twenty minutes to walk there – so you had an hour and a half to get ready. You nodded to yourself, before heading off to take a quick shower. Once you were out and dry, you faced the dilemma of what to wear. Grillby’s wasn’t a super fancy place... was it? You’d never actually been inside, only walked past it once or twice. But you shouldn’t dress _too_ casual in case you showed up underdressed. You wanted to make a good impression. Eventually, you settled on a pair of black boots, some jeans, and a blouse. Not too fancy, and not too casual. You checked the time on your phone – it was just about time to leave.

* * *

 You checked your phone to see that you were about ten minutes away from Grillby’s. You were most definitely in the ‘monster side’ of town, as it had been unofficially dubbed. This wasn’t the first time you’d been here – not that you came often – but it was the first time that you were so acutely aware of your own _humanness_. Everyone around you was a monster, all the homes and shops around you were owned by monsters. And people were looking at you; wondering what your business here was. Looking at you, as if to say: what is this human doing here? You didn’t feel antagonised or aggressed, per se. More like... people were confused. Curious.

You brushed it off and kept walking. Hopefully Alphys and Undyne would be there by the time you got there – so you could distract yourself with conversation rather than awkwardly feeling everyone’s gazes on you.

It wasn’t much longer before an unmistakable rough voice met your ears. “So then I told him to just SUCK IT UP!” Yep. Definitely Undyne. You rushed around the corner, eager to meet your friends. Alphys was the first to notice you, her eyes lighting up as she waved you over. Undyne had her back to you at first, but at Alphys’ wave, turned to you as a shark-like grin split her face. “NERD!” she greeted you enthusiastically, waving you over as well. It looked like it was just the two of them so far – evidently their friends hadn’t arrived yet. “Hey guys!” you greeted them with a small smile.

“W-we should go inside now,” Alphys said, “Sans and Papyrus will j-join us inside when they get here.” Sans and Papyrus... they must have been their friends.

“Ok, sweet.” You agreed as the three of you entered the restaurant.

The first thing you noticed once you were inside was that Grillby’s was _packed_. It was obviously quite popular. The second thing you noticed was that you were the only human there. _Stop it!_ You chided yourself. You had to stop consciously making distinctions between humans and monsters. So what if you were the only human here? You certainly weren’t the only _person_ here. With that thought, you followed Undyne and Alphys as they led you to a large booth in the corner of the room.

“You know, I’ve never actually been in here before.” You told them. Undyne cackled in response. “Yeah, that’s not surprising. We don’t get many humans here.”

“B-but it’s good that you’re here, Y/N” Alphys cut in softly. “Even if it is a l-little out of your comfort zone.” You nodded in agreement, leaning back in your seat.

“ANYWAY!” Undyne yelled, slapping her webbed palms on the table, “Forget the serious stuff. We’re here to have fun!” You laughed at her ham-fisted attempt to change the topic but went along with it.

“So, these friends who are coming... Sans and Papyrus?” you asked, “Tell me a little about them before they show up.”

“heh. too late, kid.” A deep voice came from behind you, making you jump. To your astonishment, you were faced with two skeletons. Or – not quite skeletons. Their proportions were a little different, and they seemed a lot more animated and expressive than actual skeletons. The one who had just spoken was short (probably a little shorter than you) and wore a large blue hoodie, and an even larger grin. The other one was _massive_ – he had to be at least seven feet tall and was kind of intimidating. Until he opened his mouth.

“HUMAN!” he greeted you, before bending down and lifting you out of your seat into a hug “IT IS NICE TO MEET YOU.” Embarrassingly, you let out an involuntary squeal when your feet left the ground. You tried to play it cool, though. “Uh, thanks! It’s nice to meet you too. Both of you.” You shot a quick smile at the other monster. The taller skeleton put you back down gently, as you continued. “My name’s Y/N.”

“HELLO, Y/N. I AM THE GREAT PAPYRUS!” the tall one mentioned with a flourish. “AND THIS IS MY BROTHER, SANS.” He gestured to the shorter one. Sans nodded to you in greeting.

“Sit down, noobs!” Undyne stood from her seat opposite you wringing Papyrus into a headlock and pulling him down into the seat next to her. Sans opted to take the seat to your left.

You began scanning the menu, trying to quickly decide on what to order. Everyone else at the table already seemed to know what they wanted without having to look at the menu. Grillby’s seemed like a classic, fast-food burger joint to you. _Perfect_. You were in the mood for some unhealthy, greasy food right now. But there were so many choices! You felt a nudge on your left arm, turning to see Sans grinning at you. You wondered idly if he was actually smiling, or if that was just the way his face was. “i’d recommend the classic beef burger. it’s the best thing here. **tibia** honest, i don’t think anyone ever orders anything else.” You snorted at the terrible pun but smiled gratefully at him. “Thanks. Classic beef burger it is, then.”

A monster with a giraffe-like neck came over to take orders (and Sans was right – _everyone_ ordered the classic beef burger). As the group settled into casual conversation – well, as casual as it could get with two personalities as eccentric as Undyne and Papyrus’ – you felt the tension in your body melt away. You had been so anxious that these monsters wouldn’t like you, but they were surprisingly chill.

It was only about twenty minutes before all the food came, and those twenty minutes were filled with light conversation, introductions, laughs, and _terrible_ skeleton puns from Sans (followed by indignant screeching from Papyrus). All in all, it was a lot of fun.

When the food did come to the table, you couldn’t help but notice how good it looked and smelled. You paused for a moment, looking at the two skeleton monsters. How did they eat? Wouldn’t the food just, like... fall out? You were tempted to ask, but you weren’t sure if that would be rude. You picked up your own burger and took a bite. It was amazing – you had never tasted anything like it before. Well, it tasted like a burger, but as soon as you swallowed it, you felt a strange but pleasant tingling sensation in your throat. It may have been your imagination, but it seemed like the food might have been... dissolving before it actually reached your stomach. Alphys seemed to notice your confused delight, because she leaned over the table to explain. “A-all monster food is made from magic. It’s not l-like human food, in that way. Magic food doesn’t n-need to be physically digested, either.” You felt your eyes widen in surprise. “B-but!” Alphys continued, “It’ll still f-fill you up. It gives you energy, j-just like human food.”

“Wow,” you breathed. “I never knew that. It tastes so good! This is the first time I’ve eaten monster food, to be honest.” You admitted.

“IT IS GOOD THAT YOU ARE WILLING TO HAVE NEW EXPERIENCES,” Papyrus beamed at you, “I CAN MAKE YOU SOME OF MY FAMOUS SPAGHETTI, SOMETIME!” You returned his smile, before responding. “Yeah, I’d really like that.”

You were kind of shocked at the words leaving your mouth. Not because of what you had said, but because you weren’t lying, or exaggerating, or just being polite. You really did want to spend more time with these people – get to know them better. You felt that you could finally make some friends here.

“O-oh, before I forget!” Alphys piped up, “Yesterday Y/N told me she met s-someone in the Underground, when she went to get samples... W-what was the name again, Y/N?” she questioned, looking perturbed that she had already forgotten.

This was perfect! One of them might know who Gaster was. “He said that his name was W.D. Gaster.” You told them, scanning everyone’s faces for any kind of recognition. A strange silence washed over the table. “THAT NAME DOES SOUND FAMILIAR,” Papyrus spoke slowly, “BUT FOR SOME REASON I CAN’T...” he trailed off, an uncharacteristically disturbed expression on his face.

“Yeah,” Undyne rasped, supporting her chin in one webbed hand as if in thought. “I think I should know who that is. Or I _did_ know who that was, but... there’s... something in the WAY!” she growled, slamming a fist on the table, clearly frustrated at her inability to articulate the problem.

This was odd. Very odd. You had thought, after Alphys had reacted this way that maybe she was just forgetful or hadn’t known Gaster well. But seeing everyone else at the table reacting the same way... Well – everyone except Sans. You turned to look at the shorter skeleton. He was staring right back at you, wearing an inscrutable expression. The lights in his eye sockets were pinpricks, boring into you. You started to feel very uneasy.

Suddenly, Sans turned from you and addressed everyone else at the table. “don’t think about it too hard.” The spell was instantly broken. It was as if Gaster had never been mentioned. Your looked at Sans, your expression betraying your awe and confusion. “dr. g tends to slip out of people’s minds.” He spoke lowly to you, so that the others, who were already engrossed in conversation again, wouldn’t hear. “he’s a **bone-afide** mystery.” You were silent. Obviously, Sans knew something about Gaster that no one else did. Or that no one else could _remember_. There was clearly more to the diminutive skeleton monster than crappy puns. You would need to speak to him at some point; alone. You let that thought rest in the back of your mind, as you re-joined the conversation.

The rest of the evening was relatively uneventful, and you were glad for it. When you had all finished your food, you split the bill and spilled out of the restaurant, gathering in a small group outside to say your goodbyes. “well paps, we should probably split.” Sans spoke, before his eyes lit up cheekily. “i don’t know about you, but i’m **bone tired**.” You and Undyne both groaned, while Alphys let out a little laugh. All of this was drowned out by Papyrus’ shrieking as he dragged his brother away by the arm. “GOODBYE HUMAN! IT WAS NICE TO MEET YOU! I APOLOGISE FOR MY BROTHER’S AWFUL PUNS!” he yelled over his shoulder, before shouting a brief goodbye to Alphys and Undyne as well.

You turned to the couple and spoke to them. “Thank you guys so much for inviting me to this! To be honest, I was pretty nervous at first, but that was a lot of fun.” You smiled, hoping to convey your honest gratitude. Undyne cackled, wrapping an arm around Alphys’ shoulder. “Don’t mention it, nerd. It’s good to get to know Alphy’s work friends better. You should come again next time!”

“Y-yeah,” Alphys chirped, “Next time we can watch anime at our place! Have you ever seen Mew Mew Kissy Cutie? Ifyouhaven’twecanallwatchittogetherandyou’llloveitit’ssoadorableandfunandthestorylineissocomplexandamazingandtheromanceissogoodand-” She cut off abruptly, blushing at her own incoherent rambling.

You didn’t understand half of what she had just said, but you were totally down to watch some anime with them. “Yeah, that would be awesome! I’ve never seen it before. Just let me know when you guys want to do it!” you grinned.

“Will do!” Undyne said, waving a hand at you. “We’d better see you next time, PUNK!”

Alphys giggled at her girlfriend’s antics, before waving goodbye to you herself as they walked off together. 

As you began the walk home, you couldn’t keep a smile off your face, because you felt like for the first time, you had a shot at making some real friends here.

**Notes for the Chapter:**

> That's chapter 6! 
> 
> I know - Gaster wasn't in this one. But don't worry, he'll be back next chapter! 
> 
> So many mysteries... why doesn't anyone remember Gaster? And why does Sans know so much?
> 
> Let me know what you guys think!


	7. The River

**Notes for the Chapter:**

> Hey guys! 
> 
> Gaster is back this chapter!!! Hope you guys enjoy :D
> 
> Thanks so much for all the support for this story so far - it means a lot.
> 
> Tumblr (to talk to me, ask me questions, all that good stuff): https://dimetrodonao3.tumblr.com/

You opened your eyes and rolled over in bed to check the time on your phone – 8:03. You still had half an hour until you actually had to get up, but you were too eager to get ready and head off for the day. Today was Monday – it had been exactly one week since your visit to the Underground, which meant that it was finally time for you to go back again for more field work. And of course, time for you to see Gaster again. 

Yawning, you stretched your back, relaxing when you felt the satisfaction of your joints popping. You wouldn’t go to the lab today; you could just head straight to Mt Ebott from here. Rising from your bed, you went about your morning routine as quickly as you could. When you were dressed and ready (you made sure to wear layers this time, so you could adapt to the harsh, variable temperatures of each area of the Underground), you shook some food into May’s tank, grabbed your backpack, and bustled out of the front door.

When you got into your car, you breathed in deeply, and started the engine. The knowledge that in about an hour’s time you would be in the Underground again filled you with exhilaration. As you started the drive, you went over the basic signs you had learned throughout the week. You didn’t know nearly enough to hold a conversation, but you could recognise a few common words and phrases, including ‘hello’, ‘goodbye’, ‘I understand’, ‘I don’t understand’, and ‘you’re signing too fast’. You had also learned how to introduce yourself and spell your own name.

You were honestly really excited to show Gaster what you’d learned. You knew it wasn’t a lot, and that you had a long way to go before you could understand him when he was signing, let alone hold a conversation in sign yourself; but it was a start. Your plan for today was pretty straightforward. You would start by walking to the Echo Flower room, where you would meet Gaster, before heading further into Waterfall to find the source of the nutrient-rich water. That was your mission, which you suspected would take up the whole day.

You squinted at the morning sunlight streaming in through the windshield, as you settled in for the long, peaceful drive.

* * *

When you had passed the security gate and were pulling up to the entrance to the mountain, you made sure to park in the shade this time. You did _not_ want to get into a burning hot car at the end of the day again. You pushed the door open and stepped out of the car, slinging your backpack onto your back. Double-checking that you had everything you needed, you swung the door shut and locked the car.

You groaned quietly at the thought of having to walk through Hotland to get to Gaster in Waterfall, wilting a little when you realised that you would have to walk through Hotland _every_ time you came here. Cursing the linear structure of the Underground, you pulled your hoodie off and tied it around your waist in preparation for the unbearable heat.

 _Might as well get this done quickly_ , you thought as you began the trek into the darkness of the cave system.

* * *

 

You scowled at the ‘WELCOME TO HOTLAND SIGN’ as you passed it, wiping sweat from your brow. Hotland was just as awful as it had been the last time, which wasn’t helped by the fact that you’d had a little trouble navigating the complex puzzles and traps that Gaster had helped you through before.

After a familiar walk through the dark, damp Waterfall cave system, you found yourself around the corner from the Echo Flower area where you had left Gaster. You felt your heartbeat speed up as you jogged into the room – you hoped he was still there. Not that he could have moved, but some irrational part of your mind was afraid that he would just be gone. You made a beeline for the spot you had left him in last time, eyes darting around the dreamlike, blue-hued cave. A sinking feeling began to overcome you when you couldn’t see him.

But your fears were quelled almost as soon as they arose. Your eyes landed on a spot on the ground; Gaster was sitting there, reclining against the wall. The grey thing was on the ground in front of him, its metallic, grey surface shifting in waves. When he was sitting like this, he was dwarfed by the Echo flowers around him, although you remembered that he was substantially taller than them when he was standing. He didn’t seem to have noticed you yet; his eyes – _were they even eyes? Eye-sockets? –_ were turned to the ceiling, entranced by the glimmering crystals that sprouted from it. You were reminded of last week, when Gaster had been similarly captivated by the Echo Flowers. He seemed to have such a sense of wonder when it came to the world around him; although you supposed it made sense given that he had been stuck only seeing lava and rocks for _at least_ four years.

You walked up to him slowly, the familiar static hum reaching your ears and your vision darkening around the edges. He noticed you and stood up, turning to face you. His face lit up at the sight of you, obviously relieved that you hadn’t forgotten about him. You mirrored his smile, signing ‘hello’ to him as you got closer. He looked startled for a second, but then his smile widened as he signed ‘hello’ back. You hadn’t really learned enough sign to carry the conversation much further, so you switched to speech. “I learned a little sign language over the last week. I haven’t learned that much yet, but I want to keep going with it and learn more, so you eventually won’t have to use the notebook.”

He looked touched at your efforts to learn, and signed a quick ‘thank you’. Obviously realising that your sign language was pretty limited, he picked up the notebook which you had left with him last week and began to write.

**I appreciate that you are making an effort to learn to speak with me properly. If you would like, I could help you to learn more.**

“That would be great!” you brightened, “It’d be way more helpful to have an actual person helping me learn. I’ve just been watching videos and stuff so far.” You confessed. He nodded and wrote something else down.

**In that case, I would be glad to help. Are you going to be taking more samples today?**

“No,” you told him, “today I thought we’d stay in Waterfall and look for the source of the water in this part of the system. I analysed the samples we took from here last week and as it turns out, the water is abnormally nutrient-rich, and I want to find out where it’s all coming from. I think that might be an important aspect of the environmental pressures down here.” Gaster looked mildly excited at this. He scribbled something down in the notebook.

**That is interesting – as a physicist, I have never really looked into the environment in this way. Come to think of it, I do not know the source of the water myself, nor why it is so nutrient-rich. This should be an interesting day.**

He smiled at you, awaiting a response. “It should be.” you chirped, “So, I’ll grab the grey thing, and we’ll head off?” Gaster signed ‘yes’ in response, so you reached down and gently picked up the grey object, relishing in its strange, cool feel against your palms. You opened your backpack and nestled the grey object safely inside, before starting the walk west.

Your mind lingered on the grey thing, however. You didn’t know much about Gaster at all, but the little bits and pieces you did know were very... odd, to put it mildly. Firstly, he couldn’t be seen unless you were near the grey thing. Secondly, a strange static hum and darkening vision seemed to accompany him everywhere. Thirdly, he couldn’t move away from the grey thing, or touch it. And finally, everyone seemed to have some kind of strange mental block that kept people from remembering him. Everyone except Sans, that is.

You decided if you were going to know Gaster more, you needed a few answers. So, you decided to pluck up your courage and ask. “Feel free to not answer, but I’m genuinely curious...” you hesitated as he looked at you attentively, “What exactly... is the grey thing? Why can’t you move away from it?” His expression dropped a little, and you instantly regretted asking. _Shit – what if that was a super offensive thing to ask?_ You were about to apologise, but Gaster turned to the notebook. He looked a little reluctant, and slightly hesitant, as if he wasn’t quite sure what to write, but he eventually showed you his short response.

**It is my soul.**

You tried to play it cool, but your mind was running a mile a minute at this revelation. You had someone’s _soul_ rolling around in your backpack? You supposed it made a little sense – that would explain why he couldn’t move away from it. You also knew that monster souls were all grey, unlike colourful human souls; so that made sense. But monster souls were shaped like upside-down hearts, weren’t they? This thing was definitely not. Its shape shifted and changed, and was really more spherical than anything. It also looked... small. Hurt, almost. Like it wasn’t a proper soul. And if this thing was his soul, shouldn’t it be inside him? Not just chilling in your backpack?

You decided to articulate your thoughts. “Shouldn’t your soul be... in you?” you said slowly. Gaster bowed his head briefly; he looked ashamed. He mulled over his response for a bit, before replying.

**Something happened to it, years ago. Something that cannot ever be undone. It was my own fault; my own ambition and foolishness brought me to this point.**

**I would prefer not to elaborate on that at the moment.**

You signed a quick ‘ok’ in response. Yet again, you felt as if answering one question about Gaster had brought up a million more. You felt a little guilty for upsetting him, though, and bringing down the mood. You would respect his wishes and drop the subject, but your mind kept nagging you that you _had_ to learn more. You felt like you might be able to help him; help him get to the surface, or reunite him with people he knew, or even help him fix his soul. But you couldn’t do any of that unless you knew what had happened in the first place. You decided that you would have to organise to speak with Sans as soon as possible. He was clearly your best shot at understanding Gaster.

Looking around you, you realised that you were nearing the area with the pools of bright water. You could see the faint blue glow of the algae from where you were. You picked up your pace a little, eager to get started with your work for the day. Stopping in the middle of the cave, you looked around, puzzled. Gaster looked like he was in thought as well. The water in this room was confined to pools and puddles and didn’t seem to flow to or from anywhere. So where was it coming from? It clearly wasn’t stagnant – it was drinkable and looked clean. You realised there must have been an aquifer underneath, supplying the pools with fresh water. It occurred to you that finding the water source would likely be more difficult than you anticipated.

You decided to tell Gaster your theory. “The water doesn’t seem to be flowing to or from anywhere on the surface. I think there’s probably an aquifer underneath, supplying fresh water here from somewhere else. What do you think?” He looked thoughtful, gaze moving around the room for a minute, before responding via the notebook.

**It seems you are correct. I cannot see any other way for the water to have gotten here, and to still be fresh.**

**I think I may have an idea as to where the water source that feeds the aquifer is. The large waterfall near the entrance to Snowdin flows into a river below it. It is just west of here.**

You nodded, thinking back to when you had walked past the waterfall last time. There had been a river below, flowing in this direction. You remembered that the walk to the path through the waterfall from here was uphill, which meant that the river, while well below the waterfall, could have fed adjacently into an aquifer that supplied water upwards to here. “That would make sense,” you told him contemplatively, “that must be where it comes from. So we should head to the waterfall, and find the primary source from there.” He nodded and signed ‘ok’, before you both set off towards the waterfall.

It didn’t take you very long to reach the roaring wall of water, but as soon as you did reach it, it became apparent that you had a slight problem. The river that flowed into the waterfall was considerably high up – it looked to be at least five metres above where you were standing. The cliff in front of you didn’t look safe to climb, either. There were no platforms or protruding rocks – it was mostly just a sheer rock face. 

Sighing, you turned to Gaster. “I don’t think we can get up there without a rope or something. I think I’ll have to go back to the Surface and get some climbing equipment. There’s just no way I can make it up there without anything.” You were frustrated, to say the least. You felt like you had only just gotten down here, and now you were being forced to go back up. Gaster stopped you, however, signing ‘wait’ before elaborating using the notebook.

**You may not have to return to the Surface for equipment. I can help you to get up there as I did in Hotland last week, if you would like?**

He looked a little apprehensive as he awaited your response. “Yeah!” you chirped, “That would be great. It would save so much time, and it would probably honestly be safer than me using a rope.” You were relieved – you knew that this could save hours – and it was so nice of Gaster to offer to help you. Before you could continue, Gaster frowned, looking at the height of the cliff the two of you had to scale. Was it too far? You felt your hope start to dwindle. He turned back to you, writing something in the notebook.

**There is a slight issue. The river is substantially higher than the cliff in Hotland was. I do not think I will be able to stretch my arms down far enough to reach you from the top, as I did last time.**

He paused in his writing, and you decided to interject. “That’s ok – it _is_ a lot further up. I’ll head up to go get some rope and come back down to meet you here. Hopefully we can get this done today.” You smiled at him reassuringly, trying to convey that you weren’t annoyed at him. Before you could start walking back the way you had come, Gaster shook his head quickly, signing ‘wait’ again before continuing to write.

**I could carry you as I climb up. I would not want you to waste your time when I could help you. Only if you are comfortable with that, however.**

He looked a little embarrassed, avoiding your gaze. You were embarrassed too, but you knew logically that it was the most efficient way to get things done. You rationalised that it would be safer than you making your way up with rope – you had no experience with rock climbing or anything. You nodded quickly, replying, “Y-yeah. Actually, that would be really helpful, thanks.” You moved a little closer to him, unsure exactly how this was going to work. Gaster looked a little lost as well, but he edged towards you, awkwardly outstretching his hands. He picked you up, gingerly looping one arm around your knees, the other supporting your back. You were hyper-aware of how close to him you were – the cool, fog-like feeling of him against you. Not sure what to do with your hands, you clasped them in front of your chest. 

You couldn’t bring yourself to look at him properly; not when you were so close to him. So you looked down into the blackness of his form as he reached out to the cliff with his strange little tendrils, hooking on and slowly moving up. You watched the rock of the cliff move past your face for a bit as Gaster climbed, but after a bit you felt your eyes slide up to his face. He was avoiding looking at you as well, and a faint grey colour dusted his cheeks. Was that... blush? You had no idea. You dropped your gaze again and kept your eyes on the rock until you reached the top.

As soon as Gaster had made it to the top, he carefully lowered you to the ground feet-first. He removed his hands from you, and oddly, you found yourself missing the coolness of his touch. You shrugged it off, telling yourself you were being weird. “Thanks for carrying me up here. I really appreciate it.” You told him sincerely, playing it cool. The odd grey colour had faded from his cheeks, and he signed ‘you’re welcome’ in response. You turned from Gaster to appreciate the river running by you. The water was extraordinarily clear; clear enough that you could easily see the rocks and crystals embedded on the bottom. It flowed smoothly through the soft riverbed, meandering through the rock and around the corner, where you could no longer see it. “Well,” you told Gaster, “I guess we just follow the river to the source.”

He nodded, and began to follow you as you started the walk down the river.

**Notes for the Chapter:**

> Hope you guys liked this chapter! 
> 
> Let me know what you thought. Some fun fluffy stuff is coming up soon!


	8. Agreement

**Notes for the Chapter:**

> Hey guys! 
> 
> Here's chapter 8 - hope you guys enjoy it. Some significant stuff happens this chapter...
> 
> Let me know what you think!
> 
> Tumblr (to talk to me, ask me questions, all that good stuff): https://dimetrodonao3.tumblr.com/

A soft yawn escaped your mouth as you trekked through the damp, dimly lit cave system. The river rushed by you, its bubbling and sloshing accompanying the static hum that came with walking by Gaster. The two of you had been following the river to its source for around twenty minutes now. You suspected it would have been a pretty boring walk, had it not been for the fact that Gaster had been helping you learn some more signs as you walked together. He had eagerly shown you the signs for some of the things around you – like ‘water’, ‘rocks’, ‘river’ and ‘cave’. He was also teaching you to spell in sign to make your life easier. You would have to practice all this at home so you didn’t forget it.

 _Honestly, this is a lot of fun_ , you thought to yourself as you laughed at your attempt to spell ‘river’ in sign. The sign itself was pretty easy and self-explanatory, but spelling the word out was proving a little more challenging. Gaster silently laughed along with you and showed you slowly and emphatically how to spell it properly. “Ohhhh, right.” You breathed, trying your hardest to commit the signs to memory before slowly spelling it out, looking to him for confirmation. Smiling, he flashed you a thumbs up.

You were about to ask him what the sign for ‘dark’ was, when you noticed up ahead that the river ended in a large, cavernous pool of water. You realised that this must have been the primary source of water in Waterfall. But you were a little confused – how did all of this water get here? And how could you explain all the nutrients in it? Your mind finally caught up with you, registering the sunlight streaming down onto the pool, illuminating the clear water with bright, warm light.

 _Wait... sunlight?_ In a fit of unbridled excitement, you jogged to the edge of the pool and began to wade in to get a better look. You were vaguely aware that behind you, Gaster was fretting at your impulsive action, following you out to make sure it was safe. You stopped walking out when the water reached the top of your chest, eyes cast directly above you. Many metres above you, past the vaulted ceiling in this part of the cave, you could see clear blue skies and glimpses of the vivid green foliage adorning the trees that populated the mountain. Gaster reached your side, his gaze totally focused on the small window to the surface as well. He tapped you gently on the arm, showing you something he’d written in the notebook.

**This is the first time I have ever seen the sky. It is far more vivid that I ever expected it would be.**

You were silent, absorbing the fact that he had never seen the sky before. You felt weighted down with the burden of the knowledge that it wasn’t just Gaster either – thousands of monsters had never seen the sky, never felt the warmth of the sun, never been out in the freedom of the wide, open world until four years ago. You steeled yourself, resolving that when you were done with today, you would try your hardest to convince Gaster to come to the surface with you. You didn’t think you could, with a clear conscience, leave him down here for days on end again. Tucking that decision to the back of your mind, you turned back to the issue at hand. 

“The water must get here from the surface,” you told Gaster, “I think it’s run-off that’s accumulated nutrients from the mountain. It must all come down every time it rains.” Gaster nodded thoughtfully in response, before tearing his gaze from the sky briefly to write something in the notebook.

**I think you are correct. That seems to be the most plausible explanation for how nutrient-rich the water here is.**

You took a few pictures of the area with your phone and used your GPS to mark your location so you could see where exactly on the mountain this was. You would have to climb up the mountain at some point to inspect this area from the outside. Looking around, you realised that this was all you had to do down here today. Checking your phone, you were surprised to see that it was only 11:30. You had only planned on finding the water source, and you had expected that it would take a little longer than this. You could go back up to the surface now, and maybe get some more of your lab work done – you still had a good half a day left. In that case, now was the time to convince Gaster to come with you. 

“I think I’m pretty much done for the day down here,” you began, turning towards him. You paused, shivering at the coldness of the water. “Hang on, it’s getting cold in here.” You laughed, as you both began wading back to shore. When you were out, you did your best to wring the water out of your clothes, but you were still soaked. You brushed it off, figuring that the walk back through Hotland would dry you out. Curiously, Gaster didn’t seem to be wet at all. The water had just sort of... slid off of him. He wrote something down in the notebook and showed it to you.

**Will you be leaving already, then?**

He looked a little down that you were leaving. You felt bad, but if you could convince him to come up with you to the surface you would at least feel like you had helped him in some way. “Yeah, I think I’ll head back now.” You considered your next words carefully. “Listen – I have an idea. Just... hear me out, ok?” you told him, before ploughing ahead. “I would feel terrible having to leave you down here alone again for days on end. And unlike last time, I don’t really have a plan for when I’ll be back next – it could be days, or weeks even.” You took a deep breath. “I don’t know what happened to you, or your soul, and I won’t ask, but... I do want to help you in any way I can. You seem like a good person, and you don’t deserve to be stuck down here by yourself. You could come with me to the surface! You won’t have to see or talk to anyone you don’t want to – I’ll drive us straight to my home, where it’s just me and my pet fish.” You gathered your thoughts, before continuing. “You can stay with me – that way you won’t be alone, and you’ll be able to move around and see the surface and do what you want to do... And I promise, I’ll bring you straight back down here if you change your mind, or if you decide you’d rather be down here. Besides,” you perked up, “it’ll be fun! You can get to know my pet fish, you can eat, you can chill in a place with _furniture_... You can help me learn more sign language!” you paused your lengthy outpouring, suddenly nervous. “So... what do you think?” you waited with bated breath for his response.

Gaster was silent for a few minutes, mulling over everything you had just said. You tried to guess at what he was thinking, but his expression was conflicted and indecipherable. After what seemed like an age, he met your gaze for a moment before writing a short response in the notebook.

**I appreciate that you understand that I am not ready to talk to any monsters on the surface, especially ones that I knew. But I would like to try to come to the surface with you, Y/N, if you are willing to take me with you.**

He looked very nervous, as if he was unsure whether he had made the right decision or not. You, on the other hand, were absolutely thrilled that he agreed. You would prove to him that he had made the right choice. “Really? That’s amazing!” you told him excitedly, before reassuring him, “Don’t worry. This is going to be great. There’s so much you’re going to love on the surface! And you won’t have to be alone anymore.” You smiled at him, hoping to soothe his nerves. He still looked unsure, but walked beside you as you began the walk back to your car.

* * *

 

As you thought, the walk through Hotland dried your water-logged clothes off completely. As he had when you walked by the river, Gaster helped you learn some more signs related to things around you as you made the journey back through Hotland. You had learned the signs for ‘lava’, ‘fire’ and ‘trap’ so far. Having something to concentrate on besides how much you despised the unbearable heat of Hotland definitely helped to make the trip more tolerable. While you were having a lot of fun, Gaster seemed a little distracted. Not that you could blame him – he was about to go to the surface for the first time and was probably worried about being confronted with people or things from his past. You couldn’t even imagine what was going through his head right now.

You had both finally made it through Hotland and were traversing the Castle portion of the Underground which led to the surface. It may have been your imagination, but Gaster looked oddly nostalgic as you moved through the area, gaze drifting between the immaculately polished golden walls, the reflective tiled floor and the large faux windows (you suspected magic was involved) which stretched from the ground to the vaulted ceilings far above. It didn’t take you much longer to reach the golden door, beyond which you knew lay the rocky uphill cave which would take you outside. Gaster seemed to know this as well, eyeing the door with equal parts of suspicion and reluctance.

You approached it, hauling it towards you and holding it open with your hip, gesturing for Gaster to walk through. He hesitated for a moment, but seemed to steel himself, proceeding through the door. You went through after him, letting the door shut behind you with a resounding thunk. For a few minutes straight, you walked side-by-side through the cave, trying not to slip on loose rocks and dirt. Suddenly, Gaster stopped dead beside you. You were confused for a second, stopping as well, but then realised that a pinprick of sunlight had appeared ahead. “Hey,” you started quietly, “It’s going to be fine. I promise.” Gaster looked over towards you, silent for a moment, before signing ‘ok’, and walking on towards the light.

He didn’t hesitate again as you both headed out of the cave, slowing only when you were completely outside, bathed in the warm sunlight. Gaster looked absolutely awestruck at the wide open space of the view of the town at the base of the mountain far before you – it occurred to you that he had probably never seen so much open space in his life; had never seen as far as the horizon before. The thought was almost incomprehensible to you. You had always been around open spaces, having been raised in suburban areas, never really sequestered in a city or anything. You could _not_ imagine having never seen the horizon your entire life. Again, you tried to imagine how much of an impact this must have had on all the monsters when they came to the surface for the first time. Shit, your friends – Alphys and Undyne, and even Sans and Papyrus – must have experienced this four years ago.

You decided to let Gaster absorb his surroundings for a little bit longer – you didn’t want to disturb him yet. You walked over to your car, which was just a couple of metres away (and blissfully parked in the shade), fumbling in your bag for the keys and unlocking it. You turned back to Gaster, who was still looking around him, his eyes now on the sky above you. “Careful you don’t look directly at the sun,” you warned him, “it could hurt your eyes.” He cast his eyes towards you, seemingly shaking himself out of his trance. He wrote something down in the notebook and turned it to show you. 

**It is just so difficult for me not to look at the sun. I have never seen anything like it before. It is so bright, and so far away. But you are correct – I would rather not damage my eyes.**

He smiled at you, and approached where you were standing by the car. You opened the driver’s door and got inside, as Gaster entered through the passenger side. He barely fit in the car, to your amusement – his head was touching the roof and he looked a little cramped. But he didn’t seem to mind; rather he seemed fascinated by your car. His eyes were flicking over the wheel and controls eagerly, as if trying to figure out what they were all for. _Did they have cars in the Underground?_ You honestly weren’t sure, so you decided to ask. “Did you guys have cars in the Underground?” Gaster signed ‘no’, before elaborating via the notebook.

**There was no need for cars in the Underground. As you have seen, it is a relatively small area which is easy to traverse entirely on foot. Although scrapped car parts from the Surface did fall down occasionally. I have always wondered exactly how they all fit together.**

“Yeah, I guess that makes sense.” You nodded. “I would tell you exactly how cars work, except to be honest, I don’t really know. Although I’m sure the internet will be able to help you on that front.” You realised that he probably had no idea what the internet was, so you scrambled to explain. “The internet is pretty much a human version of the Undernet. It’s basically an endless void of information.” Gaster looked excited at the prospect, as you started the car and began driving back through the winding path down the mountain.

**Notes for the Chapter:**

> That's chapter 8! 
> 
> Gaster finally came to the surface! Wonder how things will go from here...
> 
> Let me know what you thought :D


	9. The Surface

**Notes for the Chapter:**

> Hey everyone! 
> 
> So Gaster is finally on the surface! Let's see how things pan out...
> 
> Hope you guys enjoy this one.
> 
> *Also - I have a tumblr for this fic now! I'm dimetrodonao3 (https://dimetrodonao3.tumblr.com/) on tumblr (I know, very creative). I'll pretty much just post links to new chapters there, but it's also a way for people to talk to me/ask me things etc., since AO3 isn't really great for that.

The drive had been pretty uneventful so far. The road to and from Mount Ebott was never particularly busy, considering very few humans were allowed into the Underground, and most monsters had no intention of ever returning to their former prison. So you hadn’t really had to worry about anyone seeing or recognising Gaster yet – except when you’d had to ask him to duck down as you passed the security gates to the mountain. Luckily none of the soldiers really cared about what was coming _out_ of the mountain; their job was to make sure nothing got _in_ that wasn’t meant to. 

You realised that if Gaster wanted to go back, it would be more a lot more difficult to get him into the Underground than it was to get him out. You decided that you would cross that bridge if and when you got to it. Hopefully he didn’t feel the need to go back down there and be alone again. Gaster had been completely quiet throughout the ride; you weren’t sure if it was because he didn’t want to disturb you and make you look away from the road while driving, or because he was content looking out of the window in astonishment as the lush rolling hills and wide-open space shifted to the bare outskirts of the town, and then the sprawling, bustling city.

Before long, you had reached your building. The carpark was usually not very busy during the middle of the day when everyone was at school or work, so you didn’t think you’d have an issue with Gaster potentially seeing someone he didn’t want to see. You pulled into your spot, before glancing around to make sure no one was around. Satisfied that the two of you were alone, you opened your door, speaking to Gaster. “We can get out of the car here. We’ve just got to take the lift up to my floor and get into my apartment. It’s not too much further.” You reassured him. He signed ‘ok’ to you, opening his own door and sliding out, looking around him carefully. You locked up the car, and led Gaster to the lift, noting that his head nearly brushed its low roof.

The journey up was short, and when the sleek metal doors slid open before you, you leaned out to check that the hallway was empty, before stepping out and gesturing for Gaster to follow. You hurried to your apartment, fumbling with your keys before yanking the door open and bustling inside. Gaster rushed inside after you and quickly shut it behind him, letting out a silent sigh of relief that you hadn’t run into anyone on the way up.

You gestured to your humble apartment with a theatrical flourish. “Well, here it is.” You announced. “I know it’s not much, but it’s home.” Gaster smiled at you, seemingly having collected himself, and wrote something to you in the notebook.

**Your home is perfectly fine. I have to thank you for bringing me all this way and allowing me to stay here.**

“Don’t mention it,” you replied. “Come in!” He still looked a little unsure of himself and had not moved from his position pressed against the front door. He was glancing around apprehensively, as if not sure where he should go or what he should do. You decided to try and make him a bit more comfortable by introducing him to May. “Come into the living room, I want to show you something.” You told him gently, leading the way. He followed silently, eyes darting around your apartment, drinking in every detail. You stopped in front of the fish tank next to your armchair, watching as Gaster noticed May and knelt in front of the tank, eyes following her movements in fascination.

“Her name’s May.” You told him lightly. “She’s a catfish.” Gaster looked confused at this, and you remembered that monsters tended to be very _literal_ when it came to naming things. “Nothing to do with cats. That’s just what they’re called – don’t ask me why.” You chuckled. He shook his head with amusement, writing something in the notebook.

**I will never cease to be amazed at how strange human naming conventions are. You seem to have many unusual names for things which are completely unrelated to what they are.**

“Can’t argue with that,” you mused. You supposed it was true, when you thought about it. “Anyway,” you continued, “I’ll leave your soul in here so you can relax for a bit while I get some other stuff done.” You unzipped your backpack, carefully placing it on the floor. You reached in with both hands to gently grasp the shifting metallic surface of his soul, lifting it out and leaving it safely on the coffee table in the middle of the room.

Picking up your bag again, you walked into the kitchen and dumped it on the counter. You decided you’d unpack it later, before checking the fridge to start making some lunch. You hoped Gaster liked pasta, because that was all you had at the moment. It didn’t take too long to throw together a quick meal, grab some cutlery, and bring it into the living room where you had left him.

He was still seated in front of May’s tank, watching her swimming around and, to your surprise, was signing to her. you couldn’t understand a word of it though – he was going way too fast, and the few signs you could make out, you hadn’t learned yet. “... Are you talking to my fish?” you asked him, amused. He paused in his signing, looking towards you and nodding sheepishly, signing ‘yes’, before rushing to explain in the notebook.

**I know that animals on the surface are not like humans or monsters, despite the fact that some of them appear similar to some monsters, and I know that she cannot understand me. But I enjoy speaking to her anyway.**

You thought that was pretty sweet; then you realised the food was probably getting cold. “Oh, I made lunch!” you chirped. “It’s just spaghetti. It was all I really had in the fridge.” You put the plates down on the coffee table and sat on the floor in front of one. It occurred to you that you had a table in the next-door room that you could eat on, which would be a little more civilised, but Gaster seemed thoroughly fascinated by May, and you’d feel bad dragging him away. He looked towards you and smiled gratefully, signing ‘thank you’ before moving to sit on the floor opposite you, in front of the plate you had left for him on the table. You started eating – _it actually tastes pretty good_ – and Gaster followed your lead.

You realised then that you had never actually seen him eat before. What had he eaten when he was stuck in Hotland for at least four years? Your thoughts began racing. Had he eaten at all? Was that possible? You knew that monsters, just like humans, needed energy in the form of food (magical or human) to survive. So how exactly had he managed? Your curiosity got the better of you, as you decided to ask. “How did you eat when you were in Hotland?” He stopped eating for a moment to write his response.

**Actually, I did not eat. There was no food.**

“What?” you blurted. “How are you alive? Monsters need to eat to survive, don’t you? Surely you need _some_ kind of energy to stay alive? Or are there some monsters who don’t need that?” You cut off your rambling. Gaster shook his head, signing ‘no’ before elaborating via the notebook.

**I cannot starve because of what happened to my soul. But it feels wonderful to eat again.**

You nodded slowly but didn’t say anything. Your mind was bursting with questions and theories, but you knew that asking him what happened to his soul would only upset him. You _really_ needed to talk to Sans. You quickly finished off the last of your pasta, noting that Gaster had finished his already. You picked up the plates and stacked them to take them into the kitchen, calling to Gaster over your shoulder “I’ll bring my laptop over so I can set you up with the internet like I promised. You’ll love it – infinite knowledge at your fingertips!” you grabbed your laptop from your bag on the kitchen counter and brought it over to him, putting it in front of him on the coffee table and pulling up Google.

He was positively glowing with excitement, signing ‘thank you’ and writing something in the notebook.

**I cannot tell you how eager I am to learn more about human technology. Much of it has been a mystery to monsters for centuries; we were left only with remnants and scraps that fell into the Underground.**

**I am curious as to whether anyone is attempting to build a version of the Core on the surface to assist with the energy problem you mentioned to me last week. I believe that it could certainly be done.**

You grinned, glad that he was so eager to learn. “Awesome. Let me know what you find out – I’m going to the lab for the afternoon so I can get a little more work done and start writing up my findings from today’s work. I should be back in a few hours – you’ll be fine here, right?” you asked. Gaster signed ‘yes’, and you went to grab your bag off the kitchen counter and your lab coat from the hook on the wall. “I’ll see you later!” He signed ‘goodbye’ in response, waving to you as you walked through the front door.

* * *

 You buzzed yourself into your lab, putting your things down on the bench. Honestly, you didn’t really need to come to the lab today – you had planned on spending the whole day in the Underground, finding the water source – but you wanted to talk to Alphys and figure out a way to speak to Sans. Plus, you figured it really couldn’t hurt to get some more work done. You knew your supervisor would be coming around any day now to check up on your progress.

Pulling your hair into a quick ponytail, you left your lab briefly to go talk to your scaly neighbour. You knocked on her door softly, and pushed it open upon hearing Alphys’ quiet “C-come in!” Scanning the lab, you saw that Alphys was tinkering with some complicated-looking device on her bench. As was your unofficial custom, you looked around to pick out one of Alphys’ inventions to ask her about. Your eyes set on a small black box that looked kind of like a speaker. “Hey Alphys, it’s me,” you greeted her, and she turned around to face you, a smile lighting up her face. “What does this one do?” you asked her, gesturing towards the device.

Alphys made her way over to you, navigating the patches of ground that weren’t stacked with papers and inventions. “T-that,” she stuttered, “is a voice modulator. F-for Mettaton, you know? It’s not strictly w-work stuff... But! It helps him adopt different v-voices, like for performances and t-things.” You perked up, instantly intrigued. You knew that Alphys had created the robot superstar, which was _so_ cool to you – Mettaton was definitely more popular among monsters than humans, but he was still insanely famous. Apparently he visited Alphys in her lab occasionally, but you had yet to ever see him in person.

“That’s awesome!” you gushed, “Man, Mettaton is so lucky to have you around.” Alphys ducked her head at your compliment, wringing her hands together.

“S-so how’s your work going, Y/N? You went back to the Underground today, didn’t you?” she questioned, seeming like she wanted to divert the attention from herself.

“Yeah,” you brightened at the prospect of talking about your research, “I did. I ended up finding the source of the water in Waterfall, so that was great! I’ve got a bit of analysis and some writing to finish off though.” You weren’t sure how to approach asking Alphys for some way to contact Sans. It was a little weird, you knew, especially since you’d decided not to tell her any more about Gaster. But you had this unshakable feeling that Sans had all the answers you were looking for.

“Hey, so...” you began slowly, still unsure how you were going to approach this. “I really enjoyed that dinner last week, and I’ve been thinking... I kind of want to get to know Sans and Papyrus a bit better. They seem cool, and... you know, if I’m going to be hanging out with you guys more often, I...” you trailed off for a bit, before picking back up, “I was wondering if you could give me like, a phone number? Or an email address or something? So I can get in contact, you know?” you shut your mouth abruptly, glancing at Alphys to assess whether or not you had weirded her out.

On the contrary, the lizard monster beamed at you, and you felt the tension melt out of your body. “O-of course!” she turned to grab a notebook from her bench, ripping out a page and writing something down. “You know, Y/N, I was a l-little worried that you would feel out of place around all of us. It was a-actually Undyne’s idea to introduce you. B-but! I’m so glad you like Sans and Papyrus!” she stumbled over her words in excitement. She extended a clawed hand to you, to hand you the paper. You accepted it gratefully, noting that she had written both of the skeleton monster’s numbers down.

“Thanks so much, Alphys!” you told her with genuine gratitude. “I should get back to my work, but I’ll see you around.”

“Y-yeah, see you!” Alphys responded, giving you a quick wave before turning back to her work.

As you left her lab to get back to your own, you couldn’t believe that that had worked. You were sure if it was anyone but Alphys, they would have found your awkward rambling odd and suspicious. But the truth was, even though you _had_ wanted the phone numbers so you could talk to Sans about Gaster, you really did want to get to know them better. But you could worry about that once you had Gaster sorted out. With that thought in mind, you figured that there was no better time than the present to contact Sans and arrange to meet up. So you pulled your phone out of your lab coat pocket, saved both numbers as contacts, and typed a quick message to Sans.

**Hi! This is Y/N – Alphys and Undyne’s friend, from dinner last week. This might seem a little strange, but I was wondering if we could meet up at some point this week? It’s just that when I mentioned W.D. Gaster at dinner, no one seemed to remember him except you. I have so many questions, and I don’t really know where else to turn.**

You quickly pressed ‘send’ before you could start second-guessing yourself and psyching yourself out of sending the message. _There_. The deed was done. Reading over your message again, it occurred to you that you had never asked Gaster what the W.D. stood for. You decided that you really should do that when you got home this afternoon.

You settled down at your lab bench, prepared for the next few hours of work. And after that, maybe you’d get some answers.

**Notes for the Chapter:**

> So - we've got a meeting with Sans on the horizon! 
> 
> And reader is hopefully going to learn what W.D. stands for soon :D
> 
> Let me know what you all thought of this one! I really love reading all your comments.


	10. Home, Sweet Home

**Notes for the Chapter:**

> Hi everyone! 
> 
> In this chapter, reader learns a few things about Gaster and gets a reply from Sans.
> 
> Hope you all enjoy it :D
> 
> Tumblr (to talk to me, ask me questions, all that good stuff): https://dimetrodonao3.tumblr.com/

You tapped your foot impatiently as you waited for the lift to arrive at your floor. It had been a bit of a slow afternoon at the lab – you had mainly been writing a report of your findings about the water source and doing a bit of analysis on its location on the mountain. You were also looking at the kinds of geographical features might influence the movement and qualities of the water. Honestly, you were just eager to get back home, make sure Gaster was ok, and have dinner. Speaking of dinner, you’d picked up some Thai takeaway on the way back home that smelled _delicious_. You seriously couldn’t wait to get home and eat it.

When the lift’s doors slid open, you slipped out and quickly walked over to your door, unlocking it, and making a beeline for the living room where you had left Gaster. To your relief, the now familiar darkened vision and low static hum met you before you turned the corner to the living room. He was still seated on the floor by the coffee table, May’s tank beside him, and your laptop in front of him. It seemed like he was totally engrossed in whatever he was looking at; he hadn’t even realised that you were there. His gaze was fixed on the screen, and his eyes were darting around; clearly, he was reading something.

“Hi, Gaster!” you greeted him cheerfully. Immediately his head whipped around to look at you, startled that he hadn’t noticed you. He mirrored your smile, signing ‘hello’. “Looks like you managed to find something interesting.” You teased, nodding towards the laptop. He signed ‘yes’ in response, before elaborating through the notebook.

**I have done some investigation on the Core as it could be implemented on the surface. From what I have found, it seems that scientists both monster and human have been looking into constructing a version of the Core here. However, there is an issue – apparently no monsters can remember exactly how the Core was built.**

You were confused, to say the least. “How can that be, though?” you questioned, “I mean, _someone_ must have made the Core. Someone must have designed it, people must have built it...” Gaster looked down and was quiet. After a moment of deliberation, he picked up his pen and wrote something into the notebook.

**I should confess; I was the one who created the Core. I devised the idea, designed it myself, oversaw its construction, and supervised the way it was run. Others were involved, of course, but much of it can be attributed to myself.**

You didn’t know what to say – you were shocked. You figured that he was involved in the Core somehow from the way he had spoken about it last week with a sense of pride, but... for him to be the sole mind behind its design? That was _crazy_. You knew Gaster must have been smart; he was a physicist, and you were pretty sure he had a PhD – Sans had called him ‘Dr. G’ – but this was on a whole other level.

“But... there must be blueprints, or documents or _something_ of yours left behind? Something they could use to build the Core again up here?” you questioned, a little incredulous. Gaster shook his head, before responding.

**If anyone recovered the designs and documents when my lab was cleared out, they must have been disposed of or lost. Otherwise they would surely have been used already to begin developing a Core on the surface.**

You supposed he must have been right. Which meant, essentially, that he was the only one who could design a version of the Core for the surface. At least, the only one who would be able to do it sometime in the next few years. Except, he didn’t want anyone but you to know that he was alive, and he was evidently too apprehensive to venture out into public where he might be recognised. This posed a problem. You decided that you would ask Alphys a bit more about the Core when you went to work next – she held the title of the Royal Scientist, so if anyone would know about what had happened to Gaster’s plans for the Core, she would.

“That’s really unfortunate,” you told him glumly, “all that time and work of yours, just gone.” Gaster nodded slowly in agreement. “But I’ll do some digging at work and try and find out if anyone knows what happened to it. You never know!” He signed a quick ‘ok’ but didn’t look hopeful. All of this really made you wonder, though. What the hell had actually happened to Gaster? He had to have just suddenly... disappeared, or something. How did a person just disappear? And not just disappear physically, but in everyone’s minds as well. It was completely inexplicable to you.

“Anyway,” you began to change the subject to lighten the mood, “what else have you been doing?” Gaster perked up, eager to discuss what he’d learned. He began scribbling something down hastily in the notebook.

**I was curious after seeing your car as to how it worked, so that is what I have been researching for the majority of the afternoon. I am fascinated by your use of combustion chambers in cars’ engines – the notion of small, controlled explosions being utilised to power a vehicle. I find it very clever, and quite innovative. I still have much to learn about human technology.**

You couldn’t help but grin at how enthusiastic he was. “That is pretty interesting, actually. I guess I just take our technology for granted – it’s not really my area of expertise or anything, so I’ve rarely actually looked into how things work.” Suddenly, the thought popped into your head that you’d told yourself at work that you would ask Gaster what the W.D. stood for. You really should have done it already by this point, but every time you reminded yourself to ask, you just sort of forgot to.

“Oh!” you blurted, “So I kind of never asked you, but when you introduced yourself to me, you told me your name was W.D. Gaster. I feel like such an idiot for never asking, but what does the W.D. actually stand for? Like, is it your first name? I’ve just kind of been thinking of you as Gaster this whole time.” He smiled in understanding, before writing his response down.

**It stands for Wingdings. It is my first name, but I have always found it to be a bit ridiculous. For that reason, I do not usually tell it to people, especially upon first meetings.**

Wingdings? That was _adorable_. “I don’t think it’s ridiculous at all.” You reassured him genuinely, “Honestly, I think it suits you perfectly.” He looked down, seemingly flattered at your words; that strange dark grey colour was dusting his cheeks. You were fairly certain by this point that that meant he was blushing. _His name does suit him perfectly – it’s sweet._ You thought absently. _But_ , your rational mind chimed, _if he doesn’t like it, you shouldn’t use it, out of respect._

You were startled out of your thoughts by the embarrassingly loud sound of your stomach growling. Gaster stared at you, a concerned expression on his face. “Don’t worry!” you laughed at his confusion, “It’s a normal human thing. It just means that I’m hungry.” You held up the Thai takeaway that was still in your left hand (and was probably getting cold). “I bought this on the way home. You ready to eat?” Gaster signed ‘yes’, standing from his position on the ground and writing something in the notebook.

**I am eager to try more human food. And considering that you are hungry, we should certainly eat soon.**

“Ok – let’s head over to the dining table this time.” You suggested, waiting for him to sign ‘ok’, before dumping your work bag on the floor and carefully scooping up Gaster’s soul with your now free arm. Holding the shifting metallic orb against you so you didn’t drop it, you walked into your kitchen/dining area. Gaster followed, and you saw him sign a quick ‘goodbye’ to May as you both left the living room. You placed the bag of takeaway down in the middle of the table, before gently putting Gaster’s soul down on the table beside where he would sit.

You bustled into the kitchen to grab some plates and cutlery, and when you returned to the table you noticed that Gaster had taken the food out of the bag, opened the containers, and laid them out on the table. You both served some food and began to eat. The food was _good_ , and you were so damn hungry. Before you could start a conversation though, your phone beeped, vibrating against your leg. Your heart seemed to stop for a moment – _it must be Sans!_ – as you wrenched it from your pocket and checked your notifications.

Sure enough, it was from Sans. You had to force yourself not to read it, averting your eyes, locking the screen, and placing the phone face-down on the table. You didn’t want to read it here in front of Gaster – it would be rude to stare at your phone, plus you didn’t want to have any suspicious reactions in front of him. You really couldn’t afford to let him find out about your quest to uncover his secrets; you knew it would hurt him, and that you would lose a lot of his trust in you. Hell, it might even drive him back to the Underground.

So you pushed the thought from your mind. “Sorry, just one of my friends.” You provided a brief explanation. Gaster nodded in understanding. “I’m curious though,” you began in a light tone, “Have you ever had Thai food before? Because I know you guys had some human food fall down – like, I know Alphys had instant noodles and stuff – but you’ve probably never had proper, cooked human food before, right?” Gaster shook his head no, before writing a reply into the notebook.

**I have never eaten Thai food before. It tastes quite different from anything I have ever had in the Underground. We did have human food fall down, but as you mentioned it was mainly packaged foods; never ‘proper’ food. I must admit, I am enjoying it quite a lot.**

“Well, I always say you can’t really go wrong with Thai food.” You shrugged, grinning. Suddenly, an idea occurred to you. “There’s a whole world of different human foods out there, and you haven’t had any of them.  So why don’t I try and make a different cuisine for dinner each night so you can see what you’ve been missing out on?” you proposed, excited at the prospect of slowly introducing your friend to your world. Gaster looked just as intrigued, responding via the notebook.

**That is a wonderful idea. But I do not want to impose too far on your hospitality; so perhaps I could make dinner every second evening. I could introduce you to a variety of monster dishes as well.**

You were practically bouncing in your seat in enthusiasm. This was going to be so much fun! As ashamed as you were to admit it, the only monster food you had ever had was that burger at Grillby’s. There must have been a whole world of monster cuisine you’d been missing out on as well. “That’s a great idea!” you chirped. “Just write down a list of ingredients for me, and I’ll buy them tomorrow so you can make dinner.” You had both finished your food at this point, so Gaster signed ‘ok’ before tearing out a page from the notebook and beginning to scribble down a list. Meanwhile, you took the plates into the kitchen to dump in the sink.

While you were in the relative privacy of the kitchen, and Gaster was occupied with writing the list, you decided to check Sans’ message. You took a deep breath, before unlocking your phone and opening the text.

**hey kid. honestly, i’ve been wanting to talk to you about dr. g too. i have a skele-ton of questions to ask you as well. i’m free saturday – if you’re free we should go get lunch. **

You did a small silent victory dance – _finally_ you could make some sense of this whole thing. You had Saturdays off, so you typed out a quick response telling him you were free. You wished you could speak to him earlier – Saturday was five whole days away – but you would just have to play the waiting game. You could live with that, as long as you could rest assured that answers were on the horizon.  

As you started washing the plates in the sink, it occurred to you that you should probably figure out sleeping arrangements at some point. You didn’t have a spare room or an air mattress or anything – just the living room couch. It would be a tight fit for Gaster though, considering how tall he was. Hopefully it would be bearable for him, though. When you’d dried the plates and put them away, you returned to the dining table. Gaster stood when you arrived, handing you the now completed list of ingredients he had written. “Ah, thanks” you murmured, scanning over the list. There were a lot of unfamiliar ingredients; you’d probably have to ask Alphys for help in terms of where to buy them. “I’ll pick them up tomorrow.” You told him.

“Oh, also,” you began, “in terms of sleeping arrangements... the only thing I’ve got is the living room couch. I’m sorry – it’s probably kind of small for you, but it’s all I have at the moment.” You wrung your hands together, feeling a little stupid that you hadn’t thought of this before. You could have bought him an air mattress or something. But Gaster just waved off your apology, writing a response in the notebook.

**Do not be sorry. You are very kind to allow me to stay here. The couch will be fine.**

He paused for a moment, before writing something else.

**In fact, I feel as if I am imposing on you. Perhaps, as the least I could do, I could help you to learn some more sign language while I am here?**

“Oh, yeah! I’d love that.” You agreed, excited to learn more. “Do you want to start now? I mean I don’t really have anything I need to do this evening, so...” you trailed off hopefully. Gaster signed ‘yes’ and gestured towards the living room. You carefully picked up his soul from where it rested on the table and carried it with you back to the living room as Gaster followed. As you sat down, cross-legged next to the coffee table, placing his soul on top of said table, Gaster waved a quick ‘hello’ to May before sitting opposite you.

You settled back against the couch, ready to learn. This was going to be a long (but educational) night.

**Notes for the Chapter:**

> So... next chapter, a LOT of stuff is going to come to light! (I seriously can't wait!!)
> 
> Anyway, let me know what you all thought of this one.


	11. A Conversation

**Notes for the Chapter:**

> Here it is - Chapter 11!
> 
> I'm so excited for this one!! (and the next one tbh)
> 
> Hope you enjoy it :D
> 
> Tumblr (to talk to me, ask me questions, all that good stuff): https://dimetrodonao3.tumblr.com/

The last few days felt like they had gone by in a blur, even though so much had happened. For one, you had gotten to know Gaster a lot better; though you supposed living with someone for six days would do that. You had fallen into an easy sort of pattern, especially when it came to meals. Gaster had made dinner twice so far – on Tuesday it was a monster quiche, and on Thursday it had been some sort of noodle dish. He seemed to enjoy cooking, finding a kind of solace in the act. He was really good at it too! You had loved both meals, finding monster food so completely unique and different from anything you had ever eaten before. Honestly, you were kind of surprised that cooking was something he enjoyed and was so skilled at.

But then, you were quickly learning that despite his rather intimidating appearance, Gaster was quite the opposite. You had discovered him to be a shy, gentle, and overall sweet person. He was quiet and introspective, with a genuine thirst for knowledge and a razor-sharp mind.

You had made dinner twice as well – on Wednesday and Friday. You’d settled for making wonton soup the first night, and beef vindaloo on the second. _That_ had taught you that Gaster could not handle spice. At all. One bite and his whole face had rapidly turned a dark grey colour. _The poor guy_. Apparently, monsters didn’t really _do_ spicy food, so they were all totally unaccustomed to it. You had stored that bit of information in the back of your mind to make sure you’d never make that mistake again. Thankfully, Gaster had been completely understanding, and had been able to laugh at his own expense after the fact.

You had also learned some more sign language over the past few days, with Gaster’s help. It was mostly short phrases like ‘how are you?’, ‘I don’t know’, and ‘is it time for dinner?’. Just little things that would make day-to-day communication with Gaster a little easier without him having to constantly turn to the notebook. Speaking of the notebook, it was starting to run out of empty pages despite Gaster’s best efforts to be as space-efficient as he possibly could. So you had dug out another one from the stash of empty notebooks you had accumulated through various birthday presents and impulse buys, and given it to him.

You had also bought him a cheap air mattress after his first night staying with you; it was still far from a proper bed, but it was far better than your living room couch that barely fit him. Gaster had also taken it upon himself to feed May each day and, because he still felt like he was being a bit of a burden on you (even though you had reassured him countless times that he wasn’t), he had volunteered to help you out around the house with cleaning and such. Overall, you were having a great time living with Gaster. You hadn’t realised just how alone you were since you had moved to Ebott, until you weren’t alone anymore.

In terms of work, you had asked Alphys a couple of days ago about the blueprints for the Core, hoping that she would have some idea as to what happened to them. But it was to no avail. She had no idea what happened to them, telling you that no one could remember who created the Core, and that any plans they may have left behind were lost. She also told you that the idea of deconstructing the Core and reverse-engineering it had been considered, but it was ultimately decided to be too risky. It was incredibly complex, and no one wanted to risk destroying it. _Of course_ , you thought sardonically, _no one remembers that Gaster created the Core. Why would they?_

And that was what brought you to today – Saturday. The day you were finally meeting Sans for lunch; the day you would _finally_ get some answers. You had told Gaster this morning that you were going to meet an old high school friend for lunch; and he had bought the excuse without question. Since you had the whole day off, this morning you had decided to introduce Gaster to the wonders of Star Wars. You had both just finished watching ‘A New Hope’, and you turned to face him on the couch as the end credits rolled, keen to hear his reaction. He turned towards you in turn, scribbling something down in the notebook.

**I see why this series is so popular, and why you are so fond of it. I enjoyed it a great deal – the concepts and technology devised are fascinating to me. Especially the idea of lightsabers: a discontinuous beam of light strong enough to melt metal. And space travel! While we were trapped Underground, monsters could only dream of even seeing the stars. But the notion of actually vising them...**

He beamed at the thought. “I’m so glad you like it!” you clapped your hands together excitedly. “There are seven more movies in the series! We should try and watch them all.” You suggested.

Gaster looked shocked at the mention of _seven_ more movies, but eagerly signed “Yes, we should!”

You checked the time on your phone quickly; it was time for you to go. Suddenly, the calm happiness brought about by watching one of your favourite movies with your friend was replaced by jittery anxiousness. Gaster seemed to notice this, because a concerned look washed over him. “It’s time for me to go,” you explained. “I’m just nervous because I haven’t seen this friend in a while. I just hope everything goes well.” Guilt welled up in you for lying to him, but you knew you had to. Gaster reassured you through the notebook.

**I am sure everything will go well; you are a good conversationalist. I hope you have a nice lunch.**

“Thanks.” You gave him a half-smile. “See you later, Gaster. Bye May!” you called out as you walked to the door. You had slowly gotten into the habit of saying ‘hello’ and ‘goodbye’ to your little catfish from seeing Gaster do it so often. “Goodbye, Y/N.” he signed to you as you left the apartment with a wave. 

* * *

The walk to Grillby’s was pretty uneventful. But then again, that may have just been because you were too caught up in your own head to notice anything around you. Your mind was whirring, and your heart felt like it was going to leap out of your chest. Not just because you were relieved that you were hopefully finally going to learn about what happened to Gaster, but because you were scared. You were scared that Sans might not have any answers. And worse – you were scared that he did have the answers, and that the answers might be things you didn’t want to hear.

Gaster had mentioned, several times, that he had done something terrible. As much as you wanted to believe that he was just exaggerating and was holding himself to absurd standards... what if he wasn’t? What if you were forced to completely re-evaluate the way you had come to see Gaster? Just when you were really starting to like him, and genuinely consider him a friend? 

Before you could start spiralling into more hypotheticals, you realised you had reached Grillby’s. You stopped outside, leaning against the facade of the building – it didn’t look like Sans was here yet. Looking to your left, you scanned the street for any sight of Sans, but didn’t see any. You turned your head to the right to do the same, when suddenly you heard a voice back to your left.

“hey kid.”

You jumped, whirling around to face the grinning skeleton monster. How had he gotten to you so quickly? You had _just_ looked over there. “Hi, Sans.” You breathed through your shock. “Let’s go inside?” He nodded in response, following you in. You both moved over to a booth in silence, sitting down. A monster with orange, glowing flames for a head came over immediately to pour you both some water and take your orders. You couldn’t help but wonder how his glasses stayed put on his face, and how his clothes weren’t burning. Magic, you supposed. “hey grillbz. i’ll get my usual.” Sans greeted him. So _this_ was Grillby – he must own the place, you reasoned. “Can I get a classic beef burger?” you spoke, remembering Sans’ advice from last week. Grillby nodded in response, before walking back to the bar.

“so,” Sans began, “i’ve got a feelin’ you’ve got a **skeleton** in your closet. somethin’ you’re hidin’ from everyone. tell me – where’d you find dr. g?”

You swallowed. “Well, I was doing some fieldwork down in the Underground – it was my first day down there. I was in Hotland, sitting on a ledge of rock above the lava and... I saw this small grey thing on a rock platform far down below me. It was moving a little, so I thought I could sample it and I went down there to take a look. When I got closer to it, I could see Gaster.” You shrugged, before continuing. “I was terrified at first, but then I realised he wasn’t a threat, so...” you trailed off, not really sure what more to add.

“hotland... on a damn rock platform...” Sans chuckled humourlessly, then was silent for a moment. “just to be sure we’re talkin’ about the same dr. g – describe him real quick.”

“Ok,” you nodded, “he’s pretty tall, he has kind of an amorphous shape... mostly pitch black, but with a white face. He’s got white hands too, with holes in his palms. He also has like, cracks in his face... here” you drew a line with your finger from the top of your right eye to your forehead, “and here.” You drew another line from the bottom of your left eye to your mouth. “He’s also a huge dork.” You added with a half-smile.

Sans nodded. “sounds a little different, but that’s him alright. though he would look a little different, after what happened.” You decided then that you couldn’t hold back your curiosity any more. It was your turn to ask questions. “I need to know,” you stated with determination, “what happened to Gaster? What happened to his soul?” You waited with bated breath, as Sans remained quiet for a moment, seemingly gathering his thoughts.

When he met your gaze again, his mood had sobered completely. You had a feeling he wouldn’t be making any more puns anytime soon. When he started speaking, it was in a serious, low tone as if he didn’t want anyone to overhear. “back in the day – nine years ago, now – when dr. g was royal scientist, i was his lab assistant. i helped him with a lotta his work, but when it came to the core... that thing was like his baby, y’know? he was extremely protective and proud of it. not that he didn’t have a right to be – it’s a damn impressive system.” Sans paused for a moment, sighing deeply. “but he wanted it to be _his_ creation, and his alone. so he wouldn’t let me or anyone else have anythin’ to do with it. sure enough, dr. g got totally sucked into his own work. became a total recluse... allowed the core to consume his whole life.” Sans paused again, to take a sip of his water.

You stayed silent, trying to absorb everything you were hearing. “but he finished the damn thing, and it worked. and he was so proud of it too, at first. but if there’s anythin’ i know about dr. g, it’s that he’s too ambitious for his own good. pretty soon, the core as it was wasn’t good enough for him. he wanted to make it better and better; faster, more efficient, more powerful.” Sans sounded frustrated, resting his skull in his hand for a moment before continuing. “he started messin’ with shit he shouldn’t’ve. quantum shit that none of us understood.” He stopped speaking when Grillby approached with your food. The fire monster placed the plates down in front of you, giving you a brief nod at your murmured “Thanks.” Sans doused his food with ketchup but made no move to eat anything. You weren’t very hungry anymore either, but you forced yourself to slowly munch on some of the golden fries as Sans continued speaking when Grillby was out of earshot.

“i should mention – dr. g never told me any of this himself.” You detected a hint of bitterness in his voice, “i only found a lot of this out after the fact. after he was gone. i read his journal entries and scoured his lab – just so i could know what the hell happened, y’know? we were barely workin’ together anymore by the end of it. but anyway, i’m gettin’ ahead of myself." Sans paused as if to reorder his thoughts. “i was worried about dr. g and how far he was spirallin’ into his work. hell, so was everyone else. asgore himself was gonna intervene. alphys saw dr. g as a kind of mentor before she became royal scientist – she was damn worried too. but none of us acted quick enough.” You heard true regret in his voice – it was clear he felt like he had failed Gaster.

“in messin’ with things he didn’t understand, somethin’ went wrong, and... dr. g’s soul was shattered into pieces.” Sans stopped speaking, allowing you to process that. Suddenly, so much more made sense to you. That had to be why his soul didn’t look right – it was small and misshapen because it was just one piece of the whole thing. Maybe that was why you could only see him when you were near the soul piece, and why he felt not-quite solid; because he wasn’t _really_ all there. Not physically, nor in terms of his soul. He was only part of a fractured whole.

Sans took another sip of water, food still untouched, before continuing. “i only saw the aftermath. the lab was all fucked up. there’d been some kinda explosion. shit was burnin’, papers and equipment everywhere... and no sign of dr. g. i tried to find him, but he was just... gone. i can’t explain it, but... somehow i just _knew_ that a soul was shattered that day.” He paused, gaze boring into yours. Somehow you couldn’t shake the feeling that he was looking _into_ you – judging you in some way. He must have been satisfied with whatever he saw, because he kept speaking. “suddenly, no one remembered that dr. g had ever even existed. not the king ‘n queen, who made him royal scientist, not alphys, who he worked with for years, not paps, who he was always so nice to, not _anyone_. except me. don’t ask me why; i don’t know either. so i tried to figure out what happened. finally, i managed to put the pieces together – when his soul was split like that... it shifted the fabric of the whole goddamn multiverse. everything in _our_ universe was warped – sure, dr. g’s house was still there, his work was there, his damn core was still there... but otherwise it was as if he never existed. and my hypothesis is that it wasn’t just _our_ universe – the fracture would’ve erased his presence from _all_ universes.”

You stopped breathing for a second; this was so much more serious than you could ever have expected. You felt entirely out of your depth – like a child trying to get involved in grown-up talk. But apparently Sans wasn’t finished. “i looked for the pieces for _years_ , but i never found even one. and as much as i hate to admit it, one day i just... stopped lookin’. and that was that.” He met your gaze. “but then you showed up last week. and now... everything’s changed.” You took your glasses off and tried to rub the tension out of the bridge of your nose as you processed all of this. It took you a few minutes to collect your thoughts – thankfully Sans seemed to understand this, munching on his ketchup-drowned fries as he waited for you to respond. You slid your glasses back on, taking a deep breath before looking straight at Sans.

“Now that I’ve found a piece of his soul... is there anything we can do? Is there any way we can find the others?” Sans was contemplative for a bit, considering your words. “with the tech dr. g was usin’, the other pieces are probably completely scattered geographically. they won’t be near the one you found. not all of ‘em, anyway. but i don’t _think_ they’re scattered across timelines or universes. the way i understand it, the pieces should exist simultaneously in all universes and timelines – like i said, every version of dr. g would have been split at once. so technically it should be possible to find all the pieces and put ‘em back together.” You felt hope bubbling up within you, but it was quickly crushed with Sans’ next words. “but remember, kid – i searched for _years_ and never found anythin’. it was damn lucky that you found the one piece you did.”

You nodded – he was right. But then something occurred to you. “You said this happened nine years ago, right?” you had to pause briefly, because _holy shit,_ nine years was a long time. “When you stopped looking, were monsters still trapped Underground? Did you ever look on the surface?” you questioned. Sans shook his head. “no. i stopped lookin’ before we got here. but still, y/n, it’d be like lookin’ for a needle in a haystack. actually, more like a needle in a _thousand_ haystacks.” You looked down at your hands, realising that he was right. _But still_ , you thought, _I can’t do nothing. I can’t not try._

**Notes for the Chapter:**

> Well... Reader's learned a LOT this chapter. 
> 
> What did you guys think? Let me know!
> 
> (there's a really cute moment next chapter I literally cannot wait)


	12. Consequences

**Notes for the Chapter:**

> Hey everyone!   
> I'm so happy that you all seemed to like last chapter a lot... let's hope you like this one too.  
> Also - I start uni again next week, so I may have to cut back to posting once a week instead of twice. Just a maybe though. Depends on my workload, really :(
> 
> Anyway, enjoy this chapter!
> 
> Tumblr (to talk to me, ask me questions, all that good stuff): https://dimetrodonao3.tumblr.com/

_I can’t do nothing. I can’t not try._

You and Sans sat in silence for a few minutes as you both finished your burgers – although neither of you seemed able to enjoy the food in light of the conversation you’d just had. You were a little out of it, to be honest. You felt like your mind was clouded in a thick mist, like you just couldn’t _think_ properly.

So you were startled when Sans’ deep voice broke the silence, slicing through the fog in your brain. “i have to ask – is he still down there? have you talked to him since?”

“No,” you replied immediately with a shake of your head, “he isn’t down there anymore. And I’ve spoken to him plenty since then.” You paused for a moment, wondering exactly how much you should reveal to Sans. Ultimately, you decided that he was trustworthy, though. “Actually, he’s on the surface now. He’s been staying with me the last few days.” Sans looked thoroughly confused for a moment, but then perked up with interest, his eye lights brightening. You realised you’d just given him false hope that he’d be able to reunite with his old friend and rushed to explain. “Gaster doesn’t actually know I’m here with you right now.” You blurted. Sans seemed to dim a little, confused. “He was so reluctant to leave the Underground... I really had to work hard to convince him to come up here. He told me that he isn’t ready to face anyone he used to know down there, and I promised him he wouldn’t have to.” You explained, feeling terrible as you saw Sans’ hope fade completely. “I just had to know what happened to him. I knew _something_ happened, and I couldn’t help but wonder if it was something I could help fix. I don’t know, it’s stupid...” you trailed off briefly, before finishing your explanation. “I came to speak to you in secret. You were the only other person who seemed to know anything about him. So, I lied and told him I was meeting an old high school friend for lunch.” 

You watched Sans’ features for a reaction. He just nodded, and then asked you bluntly: “why do you care so much? dr. g isn’t your responsibility. you could just go on with your life without havin’ to deal with the problems he created for himself, and no one would be any the wiser. hell, I wouldn’t blame you.” You felt a wave of red anger surge within you. How could Sans have so little compassion for his friend? But the anger receded as you noticed that Sans was looking _into_ you again with that odd expression – he was testing you.

You straightened your back and told the truth. “I care because he’s my friend. And I want to help him. He’s mentioned to me several times that he’s done something terrible that he regrets, and it’s clear to me that it-’s really tearing him up inside and has _been_ tearing him up for years.” You cringed at your wording. _Tearing him up; really?_ “Sorry – no pun intended.” Sans cracked a grin. You shook off your mistake and kept talking. “I just... I can’t pretend that everything’s fine, and that there’s nothing I can do when I haven’t even tried.” You shut your mouth, watching the skeleton monster. The intensity of his gaze dropped off; he didn’t say anything, but somehow you could sense that he was satisfied with your answer.

He leaned back in his seat with a sigh. “i’ll have a think about all this. if i get any ideas on how we can help dr. g, i’ll let you know.” You nodded, before responding “Thanks. I’ll do the same.” You saw Sans hesitate for a moment, unsure of his next words, before asking, “if dr. g ever tells you he’s cool with seein’ anyone he used to know... let me know?” he stopped, before elaborating. “it’s been a while, and we didn’t end up on the best terms with all the shit about the core, but... i’d like to see him again, y’know? so would everyone else – i mean, if people saw him again, maybe they’d remember...”

You spoke quietly. “Of course, I’ll let you know.” Sans gave you a nod of appreciation, before getting Grillby’s attention to get the bill.

When the fiery bartender brought it over, you split the cost between you before walking out of the restaurant together. “y’know,” Sans turned to you, “it feels good to finally talk to someone about this. thanks, kid.” You shook your head. “No, thank _you_. I seriously needed to talk to someone about this as well.” He was quiet, before turning back away from you. “see ya, kid.” he spoke with a wave. “Bye!” you responded in kind, as you walked off to the left, and he to the right. _Wait a minute_ – Sans had come from the same direction you had, hadn’t he? Why would he walk away in the other direction? You brushed off your train of thought, figuring he must just be going somewhere different from wherever he’d come. 

You felt like you were on autopilot the entire way home, drowning out your surroundings and just walking blindly. It was difficult for you to reconcile the Gaster you had come to know with the obsessive, ambitious recluse that Sans had spoken about, who was destroyed by his own creation. Or... was it? You were snapped out of your musings when you found yourself standing outside your apartment door. It was then that you realised that you had no idea what your plan was.

Did you tell Gaster that you had met Sans? Did you tell him that you at least knew what had happened to him? But how would you explain that without mentioning that you had met Sans? Or, did you just keep up the charade that you went to lunch with a high school friend? You ran through various hypothetical scenarios in your head. Eventually, you concluded that there was no way to avoid hurting Gaster in some way. If you kept lying to him, the truth would eventually come clean (because webs of lies _always_ came tumbling down), and you would lose the trust you had earned from him and hurt his feelings badly. If you were totally straight with him and told him the truth now, he would definitely be upset with you, but you figured it would be better than drawing out the lies. Besides, you reasoned, that way you could get to actually helping him faster.

With that thought, you unlocked the front door and opened it, approaching the living room slowly. The static hum and dark ring around your vision met you before the sight of Gaster did. He was sitting in your armchair beside May’s tank, reading something on your laptop. “Hey,” you said softly, getting his attention. He turned to face you, putting the laptop on the coffee table. “Hello!” he signed cheerfully. “How was your lunch?”

You sighed deeply, before biting the bullet. “I have to tell you something.” Gaster sobered immediately, looking a little confused at your sombre mood. He was quiet, waiting for you to elaborate – he could clearly sense that this was important. “I lied to you when I told you that I was meeting an old high school friend for lunch. I actually went to speak to one of your old friends; Sans.” You stopped speaking to let that sink in. Sure enough, a myriad of emotions rapidly crossed Gaster’s features. First came shock, then confusion, hope, and finally, crushing sadness.

He looked into your eyes with a broken expression. “How?” he signed simply, before grasping the notebook to elaborate. 

**How do you know Sans? How did you know that Sans was my friend?**

Before you could answer he met your gaze again, before signing “Why?” You were starting to seriously rethink your decision. He looked absolutely crushed, giving you a searching look. You knew the only thing you could do now was explain yourself truthfully. “I was curious about your soul, and what happened to you... what the ‘terrible thing’ you said you did was.” You cursed your inability to express yourself properly under pressure, and rushed to explain yourself further. “Not out of morbid curiosity or anything – I mean, curious because I wanted to help you. I _want_ to help you.” You corrected. “I met Sans totally by accident – like a complete coincidence – at a group dinner with a mutual friend. And the fact that I met you in the Underground came up in conversation... but this was before you told me you didn’t want to see anyone you used to know yet! But I didn’t understand why no one could remember you except Sans – not Alphys, Papyrus, not anyone at that table, apparently-”

Gaster signed “Please,” gesturing for you to stop. He looked utterly despaired when he wrote in the notebook: 

**No one remembers me?**

Shit. You cursed yourself silently – now you’d really fucked up. Running your stupid mouth again without _thinking_ about what you were saying. “No.” you told him softly, before rushing to reassure him. “But Sans thinks that if people see you again, they’ll be forced to remember you!” Gaster didn’t look hopeful; in fact, he still looked absolutely devastated. “Why?” he signed again, before writing something down.

**I asked you not to make me see anyone. I am not ready.**

You felt like a piece of shit. “You don’t have to.” You told him, “That was never my intention. I even told Sans that. And no one else knows, I swear!” you were starting to panic, so you took a deep breath before continuing. “I just want to help you. And from what Sans told me today, I think I might be able to.” He wouldn’t meet your eyes, but you kept talking. “Your soul is shattered, right? Sans told me that if we can find the other pieces, we should be able to put them together and restore you to... yourself.” Again, he didn’t look hopeful. He was silent, still avoiding meeting your eyes as he wrote something in the notebook.

**It is impossible. I have resigned myself to this existence, and I must face the consequences of my actions.**

You felt awful. You stopped talking and decided to stop pushing this until you came up with an actual idea to help find the other pieces of Gaster’s soul. He caught your attention, showing you something else he’d written down.

**I would like to be alone for a bit.**

You looked down, forcing yourself not to start tearing up. Obliging to his wishes, you turned and left the living room, heading straight for your bedroom and collapsing face-down on your bed. You didn’t cry, but you felt a crushing sense of despair pervading your bones. You’d royally fucked this up.

* * *

 

You cracked your eyes open, disoriented for a moment. You must have fallen asleep. Checking the time on your phone, you saw that it was almost time for dinner. You realised that this morning, Gaster had offered to make today’s dinner, but you had left him in the living room. Plucking up your courage, you pushed yourself up from your bed and left your room, slowly making your way back to the living room. You couldn’t hide from him forever. 

Gaster was sitting on the floor beside May’s tank, watching her, but facing the doorway so that when he saw you approaching, immediately he stood. “Look, I’m-” you started, as Gaster signed “I-” at the same time. You both stopped, and Gaster gestured for you to go ahead with what you were going to say. “Look, I’m so sorry. I’m such an idiot. I put my own selfish curiosity above your needs and wishes, and I shouldn’t have done that. I should have brought it up with you first and waited until you were ready before I spoke to anyone about you.” You spoke bluntly, “But I didn’t do that. So, I understand if you don’t want to be around me anymore. If you want, I’ll take you back to the Underground, or wherever else you want to go.” You stopped your little speech as Gaster waved frantically for you to pause.

“May I speak?” he signed sincerely, meeting your gaze. You decided to keep your mouth shut, nodding in affirmation. He switched to the notebook, and you held your breath as you waited to read what he was writing.

**I will not deny that I am disappointed and upset that you spoke to Sans about me without my prior knowledge.**

You felt your heart sink, but you kept reading. 

**But I understand why you did it. And I do not want to lose your friendship; if you are still willing to accommodate me here, I would love to stay. I do not doubt that you had the purest of intentions, and that you did this with my wellbeing in mind. And while I greatly appreciate that you are trying to help me, it is not possible to restore my soul. I do not know how many pieces there are, and in a world this large... they could be anywhere.**

When you’d finished reading, you looked up to gauge Gaster’s expression. You were distressed to see that he had started to tear up a little at his perceived hopelessness at the idea of ever having a whole soul again. You resolved then and there that you _would_ find a way to help him, no matter what it took.

You hesitated for a moment, not sure if your next action would be welcomed. But you ploughed ahead anyway lest you lose your courage. You slowly stepped closer to Gaster, giving him time to move away if he wanted to. He didn’t. You flicked your gaze up to his face for a second, before gently wrapping your arms around him in a hug. He immediately froze up. For a heart-stopping second you thought you had made yet another stupid move today. But the moment passed, and Gaster wrapped his arms around you as well. Despite the coolness of his... skin? – You weren’t sure if he _had_ skin – and the fog-like feeling of his arms and body, the hug felt warm and solid. Despite the fact that your field of vision was currently all-consuming darkness (he was way too tall – you were eye level with the top of his chest), you felt light and airy as the tension melted from you completely. Despite everything you’d just done, you couldn’t help but feel like everything was going to be okay.

You both remained in the same position for what felt like an eternity – neither really willing to let go and return to the real world just yet. That was fine by you, though. You would stay here for as long as he needed you to.

**Notes for the Chapter:**

> Awwwww... not gonna lie, I love this chapter a lot.   
> Yeah, there was a little angst, but we ended on a nice fluffy note :D
> 
> Let me know what you thought!


	13. Quiet

**Notes for the Chapter:**

> Hey guys!  
> I’m officially back at uni. Luckily I think I’ll still be able to post twice a week. For now, at least. 
> 
> For those of you who are curious: there’s this chapter and one more before Reader and Gaster actually start tracking down those pesky soul pieces. 
> 
> Hope you enjoy this one!
> 
> Tumblr (to talk to me, ask me questions, all that good stuff): https://dimetrodonao3.tumblr.com/

As reluctant as you were to do so, you eventually slowly removed yourself from the hug when you realised how hungry you were. It was definitely past the time when you usually ate dinner. As you slowly drew your arms back to your sides, and took a step back, Gaster took your silent hint and did the same. After a moment of hesitation, you met his gaze. He looked like he was feeling a little better than he had been before.

“Guess it’s too late to get you to start cooking dinner now,” you chuckled, keeping your tone light. “Want to get something delivered?”

Gaster smiled sheepishly before signing his response, “Yes, that is a good idea.” Before elaborating via the notebook.

**You must be hungry by now.**

“I am!” you laughed. “I think it’s time for you to be introduced to pizza – true, greasy comfort food.” You figured comfort food was exactly what you both needed at the moment. Gaster nodded, signing “That sounds wonderful.”  
“Oh, it is.” You told him emphatically as you moved to the coffee table to grab your laptop. When you opened it and the screen flicked to life, you saw that Gaster had been looking into the Mars Rover. You hid a smile behind your hand as you opened a new tab to order the pizza.

You felt a little awkward – after the sort-of argument you’d just had, and then that hug... you weren’t really sure what to do or say. You weren’t sure exactly where you stood with Gaster at the moment. He was probably still upset at you, but was trying to push past it because he knew you had only been trying to help. Thankfully Gaster pulled you from your musings, catching your attention and showing you something he’d written in the notebook.

**Perhaps while we wait for the food to arrive, I can help you learn some more sign language?**

You nodded, grateful for the suggestion. “Yeah, that would be great. Can we do some more on the alphabet?” You were still trying to learn the alphabet in sign, so that Gaster would be able to spell names and words you didn’t know the signs for. He signed “Of course,” in response, before asking you through the notebook:

**Sign through the alphabet as accurately and as far as you can so that I can see the letters you need assistance with.**

“Ok,” you told him, before collecting your thoughts. You always had to focus really hard when it came to speaking in sign language – you couldn’t believe how effortlessly Gaster seemed to use it; he was so fluid and quick with it, like it was second nature to him. Although, you supposed, it literally was second nature to him. You began signing through the alphabet slowly, hesitating when you reached ‘K’. You always managed to forget that one. “Sorry, what’s ‘K’ again?” you asked Gaster. He raised one hand with his pointer finger and thumb pointing up, his middle finger pointing forwards, and his remaining two fingers curled towards his palm. “Ah, thanks.” You murmured, emulating his example before continuing.

Gaster had to correct your ‘R’ (you had your middle finger crossed in front of your pointer, instead of the other way around), but other than that you were doing fine. You stopped after ‘T’ though, unable to remember the last few letters. “I always seem to drop off when it comes to the last bit.” You smiled sheepishly. Gaster nodded in understanding, waving off your embarrassment before signing the remaining six letters in quick succession once, and then once again more slowly.

You slowly copied the signs. Gaster smiled at you proudly, signing “Well done!”. You grinned back. “Let me try and do the whole thing again real quick in case it was a fluke.” Concentrating on remembering the mistakes you’d made last time, you carefully made your way through the whole alphabet again, meeting Gaster’s gaze when you were finished. “That was perfect.” He signed, pleased with your progress. “I’m still pretty slow, though. I’ve got a long way to go.” You responded, trying to downplay yourself. Gaster shook his head and turned to the notebook.

**The speed at which you sign is immaterial. It only matters that you understand the signs and can use them to communicate. Remember that I have been using sign language my whole life; you have only been learning for a few weeks. With time and practice, it will come more naturally and more quickly to you.**

You smiled at his reassurance. “You’re right, I guess.”  
“Of course I am right,” he joked, grinning back. Suddenly, you were both startled by a sharp knock at the front door.  
“Must be the pizza.” You breathed, heading straight for the door and opening it. Gaster, not wanting to risk being seen, hastily ducked behind the couch.

You greeted the pizza guy briefly, took the pizzas from his arms, and thanked him before shutting the door behind you and returning to the living room. “He’s gone, you can come out now.” You told Gaster, hiding a smile at his skittishness. He rose from behind the couch, eyeing the pizza boxes with interest. He started to move towards the doorway to the living room, presumably to go into the kitchen. You stopped him with a hand on his arm, though – “It’s kind of a tradition to lounge around while you eat pizza. To be honest I don’t think I’ve ever eaten pizza while sitting at a table. We should keep watching Star Wars!” you exclaimed, rising to your tiptoes briefly in excitement.

Gaster looked puzzled at the notion of not eating dinner at a table but perked up at the mention of Star Wars. “Alright,” he signed, sitting down on the couch. You sunk down beside him, handing him a box. You’d decided to go simple and just order two plain pepperoni pizzas. You lifted the lid of your box, feasting your eyes on the cheesy goodness inside. _Perfect._ Gaster had done the same beside you and was looking at the pizza before him with intrigue (and a hint of confusion). He signed something to you that you didn’t understand. “Sorry, I didn’t understand that.” You carefully signed the phrase as you spoke – you knew he could hear you, but you figured that the more you practiced signing yourself, the easier it would be for you to understand.

Gaster began signing to you again; spelling the word this time, before doing the sign for it again so that you would remember it. “C-u-t-l-e-r-y?”  
“Oh,” you started to explain. “Well, usually we just eat pizza with our hands. If you want cutlery though, I’ll go get some.” Understanding dawned on Gaster’s features, and although he looked slightly apprehensive at the thought of eating with his hands (which silently amused you to no end), he wrote in the notebook:

**No, it is alright. If this is intended to be eaten without cutlery, I will eat it without cutlery.**

“Ok.” You told him. You found his sincerity and his genuine attempts to learn more about human cultures quite endearing. You grabbed the remote and turned on the TV, briefly got up to put ‘The Empire Strikes Back’ in and returned to your seat beside Gaster to hit play. He was hesitating to eat the pizza, so you picked up a piece of yours and began to eat it. You could see that he was watching to see how you ate so that he could do the same – he was trying to be subtle, though, so you pretended not to notice.

After a couple of seconds, out of the corner of your eye you saw him gingerly pick up a piece the same way you had and take a bite. After a moment of contemplation, he kept eating. You smiled to yourself – he liked it, then. You settled back into the couch and focussed on the movie playing in front of you, mindful of Gaster’s presence beside you.

* * *

 

After you had finished watching The Empire Strikes Back (and finished _all_ the pizza), you had both decided to take an early night and go to sleep. You’d left Gaster to his air mattress beside May’s tank and retired to your own room to get some rest.

Today was Sunday, which meant that like yesterday, you didn’t have to go to work. You decided that you would call Quinn this morning and catch up with her; you knew that being a zoo keeper she was busiest between 6 and 9am, so you would call her at 10 when things had calmed down a little.

In the meanwhile, you left your bedroom to see if Gaster was awake yet. You didn’t consider yourself a morning person but compared to him you certainly were. He usually got up a couple of hours after you – and even then, although he was _technically_ awake, it took a bit of time before he was fully alert. Sure enough, as you quietly padded into the living room, you saw that Gaster was seated on the side of the air mattress, blinking slowly. Clearly he had only just woken up.

“Good morning!” you greeted him quietly. He yawned and turned to face you, signing a slow “Good morning,” in response.  
“Let me know when you want me to move you into the kitchen so you can get some breakfast.” You told him, preparing to turn around and leave him to wake up a little more. He stood, however, and made his way over to you, rubbing his eyes before signing a brief “Now?”. You nodded in assent, carefully picking up his soul from the coffee table and ferrying it over to the kitchen, walking slowly so that he wouldn’t fall behind.

You would never admit it to him, but you found Gaster quite... _adorable_ in the mornings. He was usually so composed and eloquent and put-together; it was strangely endearing to see him like this. You didn’t think he had ever spoken in one-word sentences or asked incomplete questions when he was properly awake. Nevertheless, you left him to his own devices in the kitchen, watching him sink down into one of the stools at the benchtop.

You walked back to your room and grabbed your phone from your bedside table, unplugging it from its charger. It was just past 10:00am – the perfect time to call Quinn. So you scrolled down to her contact and rang her, seating yourself cross-legged on the foot of your bed. After a few rings, your friend picked up.

“Hey Y/N!” it was always so nice to hear the familiar sound of her voice.  
“Hi Quinn!” you responded in kind. “This isn’t a bad time, it is?”  
“No, no,” she reassured you, “I’m on my break. I should be obligation-free for the next half an hour.”  
“Good. Speaking of obligations – how are the cubs? I heard about them on the news!” you gushed. Quinn was a carnivore keeper and worked mostly with the zoo’s endangered Sun Bears – one of whom had recently given birth to three healthy cubs. It was a _huge_ deal, and you knew Quinn was just as excited about it as you were.  
“They’re amazing!” she told you, “It’s honestly such a miracle. We didn’t think we’d be able to get them to breed; not at this time of year anyway. You know, they’re tropical animals – we were thinking we’d have to build special incubated rooms for them, and everything...” she trailed off.  
“Yeah,” you scoffed good-naturedly, “I don’t know how you can survive in Canada, Quinn. It’s too damn cold all the time!” You were joking, but only partially. You and Quinn had grown up in a much warmer climate – you’d never been to Canada yourself, but you couldn’t imagine living somewhere where it snowed every winter (and sometimes even in the summer).  
“I know, I know.” she said. You swore you could _feel_ her playfully rolling her eyes through the phone.  
“Listen Quinn, you’re gonna be so proud of me” you told her, “Last week I went out to dinner with Alphys and her girlfriend and two of their friends.” You paused at Quinn’s gasp of excitement, before continuing. “And! I’ve also made friends with Gaster – the guy I told you about before, remember?”  
“Who are you and what’ve you done with Y/N?” Quinn asked with mock seriousness. “But seriously, I’m so glad you _finally_ have friends in Ebott. Life becomes so much more exciting when you have people to go out with!”  
“Well, not everyone finds it as easy as you do to make friends in a new country so quickly.” You teased, eliciting a laugh from Quinn.  
“Hey, while we’re on the topic of new countries...” Quinn began, “are you planning on making a trip back home anytime soon? To see your family and stuff?”

That was an interesting question. You paused to think – you hadn’t been home in just over a year, so you were due to pop back for a visit at some point. Besides, you were almost finished with your research for your Master’s. You might even be able to finish early. “You know, I don’t really have anything planned at the moment but I could go once I’ve finished my Master’s in a couple months.”  
“Ok, well, let me know.” Quinn told you. “We can both visit home together!”  
“Sounds good. I’ll let you know.” you responded. You stopped for a moment, contemplating, before deciding that you’d tell her about your new roommate.

“Remember how I told you about Gaster?” you asked casually.  
“Yeah,” Quinn replied slowly. “One of your new friends. The guy you found in the Underground, right?”  
“That’s the one.” You confirmed, “He’s actually staying with me on the surface right now.”  
“What?” Quinn laughed in confusion. “That so isn’t like you! He’s staying in your apartment? With you? Are you trying to tell me something?” she took on a sly tone.  
“Wait wait wait wait!” you hurried to explain. “No! No, it’s not like that! We’re friends! Just friends!”  
“... Well then why is he living with you?” Quinn teased.  
“It’s kind of complicated.” You began, “I can’t really go into it too much, but he’s kind of hiding. And he doesn’t have anywhere else to go.”  
Quinn was quiet for a moment. “Ok. Just be careful! I don’t want you getting murdered in your sleep or anything.”  
You laughed, knowing she was only half-joking. “Don’t worry, I’ll be fine. He’s very sweet. Anyway,” you quickly proceeded, lest Quinn latch onto your last statement and spin it into something it wasn’t, “I should probably let you get back to your job.”  
“Good idea,” Quinn said lightly, “I only have like 10 minutes of break left. Talk to you soon!”  
“Bye, Quinn.” You smiled, hanging up. You always felt happier after talking to Quinn – she just tended to have that effect on people.

You pushed yourself off your bed and walked out of your room again to check on Gaster in the kitchen. Thankfully he hadn’t fallen asleep again – he was eating a bowl of cereal at the kitchen counter, looking more awake. When he heard you walking in, he turned to face you and got your attention. “Y/N, I have been thinking.” He paused to write in the notebook.

**It is unfair of me to stay here in your home without contributing financially in some way. I have not had the need for money since my accident, but I do have a bank account. It has been untouched for all this time, but it should still be accessible and should still have money in it. I will give you my account details so that I can contribute.**

Your first instinct was to tell him not to worry about it, but he was right. It wouldn’t be a bad idea. You didn’t exactly have infinite money; only what you had from your scholarship and grants. And supporting two people rather than just one was more expensive than you were used to. But then you realised that there was a problem.

“I seriously appreciate that, but there’s no way I’m going to be able to go to your bank and access your account even if I do have all the details. I’m pretty sure only you can do that. I’d need ID or something... and there’s no way I’m fooling anyone into thinking that I’m you. I’m not even a monster.” You paused for a moment, wondering whether you would be pushing him too far again. “If we were going to access your account, you would have to come with me.”

Gaster was silent, thinking it over. He looked conflicted between wanting to help you financially and not wanting to leave the house at the risk of being recognised. You wanted to try and reassure and convince him, but you kept your mouth shut. You would let him decide this on his own – the last thing you wanted to do was pressure him to leave the house in the light of what had happened yesterday. After a bit of deliberation, Gaster began to write something in the notebook.

**I will go with you; but at the request that if I see someone who could recognise me, you will assist me in avoiding them.**

“Of course!” you agreed immediately. This was amazing! You were so glad Gaster was finally going to leave the apartment for a bit – he’d literally been inside all week. Not to mention, this was a chance for you to prove that Gaster could trust you again after yesterday’s events. You were determined that this would go well.

**Notes for the Chapter:**

> And that’s chapter 13! 
> 
> Next chapter is an important one - reader finally realises something a lot of you guys have been hinting at!
> 
> Let me know what you thought of this one :D


	14. An Idea

**Notes for the Chapter:**

> WOW - this is a long one. Seriously, I have no idea what happened lol
> 
> I'm not crazy about the first bit of this chapter, but it's important, I promise! Some really important stuff happens at the end as well :D I have a feeling a lot of you are going to be SHOOK at the end of this chapter. 
> 
> Hope you guys enjoy it!
> 
> Tumblr (to talk to me, ask me questions, all that good stuff): https://dimetrodonao3.tumblr.com/

You and Gaster had decided together that you would head down to the bank after lunch. That is, until you realised it was Sunday.

 “Wait a minute,” you told Gaster, “Will the bank even be open today? It’s Sunday.” He looked at you strangely, before signing in response “Of course it is open. Why would it not be?”

“It’s just that human banks generally close on Sundays. So we’d normally have to wait ‘till tomorrow.”

“Why?” he signed. He looked genuinely interested.

“Well I think it stemmed from a religious thing about not working on Sundays. I don’t know why they still keep doing it though – most businesses do open on Sundays now.” You explained. Gaster merely nodded slowly; you had a feeling he’d be doing more research into that later.

“Well, I guess it should be open then. We’ll head off after lunch?” you questioned. Gaster signed a quick ‘yes’ in response. It was pretty clear to you that his distractedness was caused by his nervousness at leaving the apartment, so you decided you’d let him be until you were ready to leave.

You busied yourself, checking on May and organising some things on your desk in your room. It was then that you realised that you were nervous, too. What if Gaster did see someone who recognised him? How would you handle that? How would _he_ handle it? You told yourself that you were being prematurely paranoid – you’d cross that bridge if and when you got to it.

In the meantime, you moved to the kitchen and started to rifle through the fridge for some ideas on what to make for lunch.

* * *

You dumped the plates into the sink, deciding you’d wash them later. You and Gaster had eaten lunch (you’d gone simple and just made sandwiches), and it was time to head off. You had been hoping that Gaster’s nervousness would lessen over the last couple of hours, but it seemed that instead the opposite had happened. He had told you that at monster banks, rather than needing a driver’s license or some other form of ID, they just scanned your soul to verify your identity. So not only was he anxious about being recognised, but he was also worried that because his soul was incomplete, it wouldn’t be able to be scanned properly.

You were trying to reassure him as best as you could, but he still seemed incredibly apprehensive. “Hey, it’s going to be fine,” you told him as you picked up his soul from the coffee table and placed it gently into your bag alongside your phone and wallet, “if your soul can’t be scanned, it doesn’t matter. I can still afford to keep us both alive.” You said jokingly, trying to lighten him up a little. He just nodded in response, seemingly unconvinced. Nevertheless, you opened the front door and stepped out, holding it open for him with your hip. After a moment of hesitation, he stepped out after you, glancing down the hall to confirm that there was no one there.

It was a short trip to the car; once he was inside, Gaster visibly relaxed a little. “What’s the bank called? Can you type the name in here?” you asked him, handing him your phone to enter the name into Google maps. He took the phone and typed ‘Bank of the Underground’ in. _Of course that’s what it’s called._ Monsters and their practical names. “Thanks,” you smiled as he handed your phone back. He signed “You’re welcome,” but still looked quite distracted, anxiously watching the carpark out of the window.

The drive was short and peaceful, but you could practically _feel_ Gaster’s mind whirring beside you the entire time. Thankfully, you found a parking spot outside the bank fairly easily. Before you got out of the car, though, you took a moment to study your surroundings. The bank ahead looked just like a normal bank – except, of course, it was full of monsters. And it really was _full_ of monsters. For a moment, the thought crossed your mind that maybe you should head back to the apartment and come back here with Gaster on a day when it was less busy. When there were less people inside who might know who he was.

But you stopped those thoughts in their tracks. You were starting to let Gaster’s nervousness bleed into you. It would be fine. “Ready to go?” you asked him, giving him a sideways glance. “Yes,” he signed, meeting your gaze. You nodded and opened your door, stepping out and shutting it firmly behind you. Gaster opened his door with a shaky hand but didn’t get out, eyes flicking around to assess who was around him.

“It’s pretty busy in there,” you spoke, trying to distract him, “which should work to our advantage. No one will notice us in the middle of a crowd like that.” He didn’t exactly seem reassured as you walked up to the revolving doors of the bank together. You stepped through and went straight for the line of people waiting to be served. You felt like if Gaster was going to be recognised today, it would be here. He seemed to come to the same realisation, because you noticed that he was standing directly behind you, as if to hide himself. Not that it mattered – he was substantially taller than you, so his face was still completely visible.

Luckily, the line seemed to be moving quickly (why couldn’t human banks be this efficient?), and everyone seemed to be too focussed on getting their own business sorted out to look at either of you. You swept your gaze around the bank, curious about how everything operated. You could see the identity-verifying soul scanners Gaster had mentioned up the front. They looked kind of like metal detectors used in airports – monsters would step through, and their soul would be scanned from within them. You had thought that they would have to bring their souls out and put them into a chamber or something to be scanned... _just like Alphys’ Soul Tracker_ , you recalled.

Your mind came to a screeching halt, homing in on your last thought. The Soul Tracker! Your thoughts began to go into overdrive as you realised the implications of the device’s existence. Alphys had told you that it could track the location of any soul, given that it had been scanned beforehand. _Maybe_ you would be able to get it from Alphys somehow. _Maybe_ Gaster would let you use it to scan his soul. _Maybe_ it would be able to show you the locations of all the other fragments as well as the one it had scanned. _Maybe,_ just maybe, you could use it to help him restore his soul.

But how would you get it? Alphys had been extremely secretive about the device – she was clearly ashamed of it; ashamed of how invasive it was and the dangerous potential it had in the wrong hands. And it wasn’t like you could actually tell her what you were using it for. She didn’t remember who Gaster was, and he had made it pretty clear that he didn’t want anyone knowing that he was still around.

 _You could steal it._ The idea crept into your mind, and you fought to rid your brain of it. You couldn’t do that! You couldn’t betray your friend’s trust in that way. It was wrong. Even if it was for a good reason. No matter how much far you shoved the idea down in your mind, however, it still lingered. It could be your only chance of helping Gaster. It could be his only chance of having his whole soul again.

You were drawn out of your thoughts when you realised that you and Gaster had reached the front of the line. _That was fast_. “How can I help you?” the teller asked with a friendly tone. Gaster began signing to him – it was too fast and there were too many unfamiliar signs for you to understand. To your surprise, the teller responded in fluent sign language. You were a little confused; did all monsters know sign language? If you had gone to a human bank, you had no doubt that the tellers wouldn’t be able to understand him. They would have had to bring in an interpreter or something.

When Gaster stepped into the ID soul scanner, you realised that you might have a problem. His soul was in your bag – not in him. Would the scanner even work? Would it be suspicious if you brought out the soul piece and put it in the machine? You decided to just wait and see what happened before you attracted suspicion. A bank was literally the worst place to make a scene. To your surprise, the machine scanned him over once, a green light illuminating him. _Well,_ you reasoned, _he must be a projection of the soul piece._ That would be why you couldn’t see him unless you were near it – so it made sense that he would be able to be scanned without any issue.

As Gaster spoke to the teller some more, you turned your attention to the rest of the room, being unable to understand most of what they were signing. To your relief, no one seemed to be looking at either of you, and no one seemed to have recognised Gaster. This was going so much better than you could have hoped! Within minutes, you felt a familiar cool touch on your shoulder. You turned to see Gaster holding up a brand-new sleek credit card. “Awesome!” you beamed, reflecting his own enthusiasm. “Shall we get out of here?” you asked, already knowing what he would say. He gave you a look as if to chide you for asking such an obvious question and signed a simple “Yes.”

You started heading towards the revolving door, walking side-by-side. Within seconds, however, Gaster froze in his tracks. _Oh shit._ Realising he must have seen someone he knew, you followed his gaze to see a tall, cat-like monster who had just come through the revolving door. You double-checked that Gaster was indeed looking at the cat monster, because he didn’t seem to have reacted to Gaster’s presence in any way, merely giving you both a cursory once-over, his yellow eyes passing over you.

Once his initial shock had worn off, though, Gaster continued on his way out of the bank. You followed, a little lost as to what had just transpired, but eager to get back home. You refrained from asking anything until you were both back inside the car, free from the risk of being recognised. Once you were in your seat with the doors shut you turned to Gaster, who still looked a little shaken. “Did you know that guy?” you questioned. He nodded slowly in response, elaborating through the notebook.

**That was one of my former neighbours from Snowdin. We were friendly – we knew each other. But he did not recognise me at all when he saw me.**

You were quiet for a minute as you processed what that meant. That guy was someone who, ordinarily, would have recognised Gaster and greeted him in some way. He had definitely _seen_ Gaster... but maybe he hadn’t recognised him or something? Or maybe he just had other things on his mind?

 _Or maybe Sans was wrong._ He had suggested that people’s memories of Gaster might be forcibly restored if they saw him again, but... apparently, that wasn’t the case. You didn’t _want_ to believe that, but some part of your mind nagged that it was going to be a lot more complicated than people’s memories being miraculously restored after laying eyes on him.

“I’m sorry.” You told him simply, taking a minute to think about your next words. “There must be another way to help people remember. I’ll help you find a way.” _You could steal the Soul Tracker._ The intrusive thought leapt to the front of your mind against your will, but you hesitated to shut it down this time. It was starting to seem like putting Gaster’s soul back together was the _only_ chance he had at living a normal life again. You would have to think more about this later.

Gaster was still quiet, presumably dwelling on his perceived hopelessness at ever being remembered again. You decided to change the topic, not wanting him to spiral. “Hey, so... that bank teller knew sign language.” You blurted awkwardly.

“Of course.” Gaster signed slowly. He looked confused as to what point you were trying to make. You seriously needed to work on your subtlety.

“Well, it’s just that if we had gone to a human bank, I’m like 100% sure the teller wouldn’t have been able to understand you. They probably would have had to get an interpreter or something. Most humans just never learn sign language. Myself included, until I met you.” You admitted, a little ashamed. Gaster took to the notebook to respond.

**Why are humans not taught sign language in school? All monsters are taught sign language in the same way they are taught spoken language. This way everyone can communicate with each other.**

You were astounded; and you felt kind of bad. Gaster must have been so confused when you hadn’t understood him at all when you’d first met. He’d probably never had to deal with people not being able to communicate with him before. “That’s... a really good point. I have no idea why we don’t learn sign language in school or anything, to be honest. Now that I think about it, it’s kind of messed up.” you told him. Gaster took to the notebook again.

**A cultural difference, I suppose.**

You sensed a joking tone in his words and huffed out a little laugh. “I guess so.” Humans were kind of shitty. “But hey, you left the apartment!” you tried to be more positive. Gaster smiled, embarrassed, and signed “Yes, I did.” Before elaborating via the notebook.

**Perhaps I will endeavour to do so again at some point in the future.**

Beaming at the progress he’d made, you started the car, and began the drive back to the apartment.

* * *

You breathed a sigh of relief as you hurried into your lab building with two minutes to spare. You’d slept through your alarm by almost half an hour, and although Gaster had heard it and wanted to wake you up so you wouldn’t be late, he was trapped in the living room because it was where his soul fragment was. And so, you had leapt from your bed in a panic and had to frenziedly rush out of the apartment with a hurried goodbye to Gaster (and May) lest you be late to work.

You planned on saying hello to Alphys (and maybe trying to figure out a way to get your hands on the Soul Tracker), but you were startled to see your supervisor, Ning, standing outside your lab. “Hi, Ning!” you greeted her, still a little breathless from your run down here. _Really?_ – you had known that she would show up to check on your progress at some point soon, but did it have to be today?

“Hello, Y/N.” Ning gave you a friendly yet professional smile as you buzzed yourself into the lab, holding the door open for her to go through first. “I guess you know why I’m here,” she chuckled, turning to face you once you were both inside.

“Yes, of course.” You affirmed, opening your laptop, placing it on the lab bench in front of her, and pulling up your thesis. “Here’s my thesis so far– let me grab my samples and lab-work together for you to look at as well.” Ning gave you a nod of assent, settling into the chair and resting her chin on her hand as she read through your work. You bustled around the lab, pulling samples out of the fridge and diagrams and printed sequences of code out of various drawers around the room, gathering them to place next to Ning on the lab bench.

After she had read your thesis, you explained all of your lab-work, samples and other bits and pieces of evidence to Ning in painstaking detail. You had worked _damn_ hard on all of this – you were so passionate about your work, and you wanted to make sure that your supervisor had the chance to appreciate it fully. You wanted her to be impressed. You wanted the _world_ to be impressed if – _when_ – you finished it and got it published. You knew you had made significant scientific progress through your research, and you needed to share it.

“This is good stuff.” Ning murmured. “Really good. I’m surprised at how much you’ve done,” she continued, eyebrows raised in thinly veiled surprise. “at this rate, you’ll almost definitely be able to finish early; well before your deadline. I wouldn’t be surprised if you were able to wrap all of this up within the next month.” You struggled to contain your enthusiasm but couldn’t help letting a wide grin slip. “Congratulations, Y/N. You’re doing really well.” Ning’s eyes met yours and she gave you a smile.

“Thank you so much!” you gushed, still beaming. You were so glad that she liked your work, and that you were in good graces with her. It was through her that you got your research money, after all. She could pull your funding at any point – but it looked like you wouldn’t have to worry about that anymore. You escorted Ning out of the lab, waving goodbye to her as she left the building. You suddenly felt totally refreshed and motivated; you felt inspired to work even harder.

Needless to say, you got a lot of work done that day.

* * *

By late afternoon, you were satisfied with the amount of work you’d done, and you pushed yourself up from your seat and began packing up your things in preparation to leave. As you pushed out of the door of your lab, it occurred to you that in all the panic and shock in the morning with your supervisor showing up, you hadn’t had the chance to say hi to Alphys. It was getting later in the day, but maybe you’d manage to catch her on her way out if you went looking for her now. 

You raised your fist as you reached her door, knocking on it sharply. Where usually you would have heard Alphys’ timid voice inviting you in, there was only silence. You tried the handle and heard a click; it was unlocked. Pushing the door open with your forearm, you called out to Alphys. “Hey, Alphys. You in here?” you questioned. No response. You stepped into the lab – all the lights were still on, and Alphys’ work hadn’t been packed up yet. Evidently she hadn’t left for the day yet; she was probably in the bathroom or something. You decided to stay where you were and wait for her to come back so you could say hi to her before you left.

It wasn’t more than a few seconds before you felt your eyes, almost against your conscious will, gravitate towards where you knew the Soul Tracker was. On your left, tucked behind various other devices of Alphys’. _No one would even notice it was gone_.

Your breath caught in your chest and your heartbeat sped up as you realised that if you were going to steal the Soul Tracker, you had to do it now. It seemed as if fate was tempting you. You might not get another chance. You desperately didn’t want to have to steal it and betray Alphys’ trust, but you couldn’t explain to her why you needed it, and she’d never give it to you. She’d told you herself that it was invasive and that she never wanted to use it again.

And what about Gaster? Sans had tried for years to find him and help him somehow but had failed and given up eventually. No one knew any way to help him; no one had any idea where the rest of his soul fragments could be, not even Gaster himself. The answer was right here, at your fingertips. You could help him be himself again. You knew that just bringing the machine home and having it work would bring so much hope to him. If there was one thing Gaster was seriously lacking right now, it was hope for himself.

It was that thought that spurred you on. You navigated the claustrophobic lab, sliding past Alphys’ large machines and stepping over tangled cords, your eyes fixed on the small white device. You pulled your laptop and some notebooks out of your bag to make room for the Soul Tracker, before carefully prising it from its hiding place. You blew the light coating of dust off of it (obviously Alphys hadn’t been lying when she said she hadn’t used it since Frisk), and carefully nestled it inside your bag, making sure its shape wasn’t too discernible in case you ran into Alphys on the way out.

You bolted out of the lab, stumbling over a stray wire, and shutting the door behind you. You didn’t look back for fear that you might see Alphys. Your feet carried you all the way outside the building before your brain kicked in.

_What the hell were you doing?_

**Notes for the Chapter:**

> We are rapidly nearing the end of the first arc of this story - just one more chapter before we get into the soul hunting arc!!
> 
> I'm so excited for next chapter!!! All my meticulous planning is gradually coming to fruition lol
> 
> Let me know what you guys thought!


	15. The Soul Tracker

**Notes for the Chapter:**

> Hey everyone! 
> 
> Before we start with this chapter, I have something I want to clear up. A few people were pretty put-off with Reader’s decision last chapter to steal Alphys’ Soul Tracker (and rightfully so – it was a terrible thing for her to do). I just want to make it clear that I’m not trying to condone her actions or make it seem like it’s totally fine that she’s just betrayed her friend’s trust and stolen from her on an impulse. 
> 
> The way I’m writing her, Reader has a problem with acting on impulse and whim, thinking she’s doing the right thing without really thinking about the humanised/personal consequences of her actions. Like when she spoke to Sans about Gaster without asking him first – she did it with the intention of helping Gaster, but without really thinking about the fact that he would probably be upset with her if she did that. In this situation, she realised that the Soul Tracker would help, and saw a chance to take it – so she did – without fully thinking through the consequences with both Alphys and Gaster. 
> 
> Rest assured, she will have serious consequences to deal with for what she’s just done. And she will learn and grow from her mistakes. A big part of Reader’s development throughout this story will be her learning to work on her impulsiveness, and learning to think about the consequences of her actions before she takes those actions. She’s a flawed character, and one of her arcs will be to seriously work through those flaws and better herself. I feel like flawed characters are much more interesting both to write about and to read about than perfect characters, so I’ve given Reader clear flaws so that she can make mistakes and develop as a person from them. 
> 
> I wrote the Soul Tracker stealing as a major turning point in the story – not just the obvious turning point, in terms of finding the locations of the soul pieces, but also as a turning point for the Reader internally. She learns from this (as well as the mistake she made talking to Sans behind Gaster’s back) that she has a problem with acting without thinking through interpersonal consequences, and she will begin to consciously and seriously work on fixing that problem. I have some stuff in terms of her backstory as well that feeds into this. 
> 
> Sorry for that massive text dump – I just wanted to make all of that clear so that people didn’t think I was making the Reader do stupid things for the sake of doing stupid things, or for the sake of moving the plot along. It all has a deeper reason and it will be addressed and resolved throughout the course of the story. 
> 
> With that said though – hope you all enjoy this chapter!
> 
> Tumblr (to talk to me, ask me questions, all that good stuff): https://dimetrodonao3.tumblr.com/

_What the hell were you doing?_

You didn’t have time to change your mind. If you turned back Alphys would be back in her lab by now, and you would have to explain why you’d taken her Soul Tracker. You ran the rest of the way home, your mind in a state of flux, scrambling to figure out what your next step was. Should you call Sans and tell him what you’d discovered? He could definitely help. No – you needed to speak to Gaster first. You wouldn’t make that mistake again. Your eyes were locked straight ahead of you the whole time as you ran down the familiar path home. You didn’t register anyone or anything around you – your sole aim was to get back home without getting caught.

You tapped your foot rapidly and clutched your bag to you while you were travelling up to your floor in the elevator. Logically, you knew that there was no way Alphys would see you with the Soul Tracker now. But you would only feel truly safe when you were in the privacy of your home. The metallic doors slid open, and you slipped through, making a final dash for your apartment door.

Bursting through, you slammed the door behind you. You leaned against it, breathing out a sigh of relief. Startled, Gaster appeared in the doorway to the living room, features forming an expression of worry. “Is everything alright?” He signed, watching you imploringly. You gathered yourself together, trying to calm your breathing from all the running you’d just done. “I’m fine,” you told him, and looked down at your bag as if to confirm that the device was still there.

A sickening feeling crept into your gut as the reality of what you had just done started to sink in. _Oh God,_ _I should not have done that._ But it was too late to take it back. You’d done it now. You would have to follow through with you had started, and deal with the fallout afterwards. Why couldn’t you just _think_ before you acted? It was becoming apparent to you that you had a serious impulse-control problem – something you knew you had to really work on. But you couldn’t dwell on that right now; you had to deal with the situation in front of you.

You raised your eyes to meet Gaster’s. He looked wholly unconvinced that you were ‘fine’ and was waiting for you to elaborate. “Ok, please hear me out.” You began, organising your thoughts and processing what you would say next. “I think I’ve found a way to help find the rest of your soul fragments. I know you think it’s not possible, but I really think I’ve found a way!” the words tumbled out of your mouth as you scrabbled with your bag to take the Soul Tracker out. You quickly assessed his expression – he didn’t look hopeful, but seemed interested in what you were saying nevertheless.

“This is a Soul Tracker.” You told Gaster once you’d freed the device from the bag, presenting it to him. “If it scans a soul, it can track the location of that soul. I think if we scan the soul piece we’ve got, it’ll be able to track the other pieces’ locations. We’ll be able to know where they all are!” Your words poured out, conveying your excitement. Gaster was looking at the machine in a new light. You saw a glimpse of hope in him; a hint that he believed that _maybe_ this machine could help him. He was still a little guarded with an air of caution, however. As if he was hesitant to have hope in something in the fear that it would fail him.

You were absolutely determined that this bloody machine would work. The last thing you wanted was for that new spark of hope in him to be crushed. “So... do you want to give it a go?” you asked him. You expected Gaster to hesitate and take some time to think, but he responded immediately, signing a simple “Yes”. He looked a little unsure, but evidently the possibility that the Soul Tracker might work was enough incentive for him.

You hesitated, though. Should you call Sans, at least to let him know what was going on? He might be able to help – it would certainly be easier if you had three minds working on this rather than just the two of you trying to work this out on your own. You pushed that out of your mind for now, though. You'd done enough stupid spur-of-the-moment things recently. Maybe you would contact him later, and only if Gaster agreed to it.

“Ok,” you nodded, “I think we just put your soul inside the little chamber, and... push one of these buttons?” Now you felt even more stupid – you didn’t actually know how to use the device. It was a glass chamber on top of a white box with a screen on the front. There were four buttons: three small grey buttons below the screen, and one larger green one beside it. Gaster seemed a little confused at your uncertainty, and asked “Where did you get this?” You paused for a moment before responding. “I got it from one of my co-workers. She made it a while ago and told me what it does recently. I knew it would help, so I brought it back.”

You were _technically_ telling the truth... but you felt absolutely terrible about the reality of how you had actually obtained the device. You had no doubt that if Gaster knew you’d stolen it he would insist that you return it. And you _would_ return it, of course, once you and Gaster had used it. You couldn't change the fact that you had stolen it, but you could at least try and make  _some_ good of this situation by using it to help Gaster. You would have to speak to Alphys as well; confess, return the device, and apologise to her for what you'd done. Thankfully, Gaster seemed to accept your explanation, because he wrote a suggestion in the notebook.

**The green button is most likely the one that will initiate the scanning process. Generally speaking, when it comes to monster technology, green signifies some sort of scanning.**

You nodded, remembering how the soul scanners at the bank had lit up green – you had thought it must signify approval, but evidently not. “Alright then!” you chirped, despite how tense you were feeling. You twisted the cylindrical glass chamber, and it hissed open at the top, the glass somehow spiralling and fragmenting to leave a hole for you to put the soul into. _Magic_ , you thought somewhat sardonically. You paused, looking up at Gaster, right into his eyes. “Are you sure you want to do this? It’s up to you – I don’t want you to do this just to appease me or whatever... I genuinely think this will work.” He simply smiled at you and signed “Yes.” He went to elaborate via the notebook.

**Although I am quite skeptical – as I am fairly certain that it is not possible to locate the other pieces of my soul – I am willing to try this. At this point, what do I have to lose?**

You studied him for a moment longer, before picking up the small, amorphous grey soul piece in both hands, and placing it into the chamber. Strangely, it didn’t rest on the bottom of the chamber; rather, it just sort of _floated_ in the centre. It looked so small and vulnerable in there – the chamber had clearly been built to house a whole soul, so there was a lot of empty space inside. When you removed your hands from the chamber, the fragmented glass at the top unfolded itself to seal the soul piece off – it looked as if the glass had never been disturbed in the first place.

Your right hand drifted towards the green button, but you stopped short just before pressing it. You turned the Soul Tracker to face Gaster instead, holding it out to him. “You should press it.” You suggested. He didn’t say anything but met your eyes and gave you a small nod of understanding. He reached out with one hand and pushed the button with a single outstretched finger.

There was a flash of green light, and then nothing. “Is that... it?” you questioned softly. “Maybe we have to push one of the other buttons?” you questioned, trying to stay calm outwardly, while inwardly you were panicking. You were hoping and praying that that was the issue, and that it wasn’t a problem with the soul piece not being complete. Gaster was looking like he was losing hope, but pressed the grey button on the left nevertheless. 

Suddenly, a grid popped up on the screen. Six green dots were scattered throughout, one of which had a black ‘X’ on it. Your heart skipped a beat. The soul pieces! You let out an involuntary squeak when you realised what this meant. Gaster looked completely dumbfounded; he was staring at the screen, uncomprehending, as if he wasn’t quite sure if what he was seeing was real.

“We did it!” you emphasised to him, grinning “We actually did it!” He looked down at you, as his expression transformed to one of pure joy and relief. You were shocked when he spontaneously pulled you into a hug, the Soul Tracker sandwiched between you as you still held it in your arms. You laughed at his enthusiasm; you were so happy that he had a chance now. And more importantly, that he _knew_ he had a chance.

Gaster released you quickly, flustered at his own actions. He began to sign an apology for his impulsiveness, but you stopped him, grasping both of his hands in yours. “You have nothing to be sorry for. This is an amazing moment! Seriously, this is a turning point for you!” you told him. He nodded in agreement, before taking to the notebook

**Thank you so much for all of your help, Y/N. If it were not for you, I would still be alone in Hotland. Thanks to you I have been able to see the Surface for myself. I have learned more about human culture and the wider world because of your help. And now, because of you, I have a chance to be whole again. A chance to be free again.**

You couldn’t meet his gaze; you could feel slight heat rising in your cheeks at his sincerity. “Don’t mention it,” you tried to brush it off. “I couldn’t _not_ try to help you.” He shook his head and wrote something else in the notebook.

**Thank you for having such perseverance with me. It is something I do not have much of for myself.**

You met his eyes this time, and you shared a brief moment of mutual unspoken gratitude. You remembered the Soul Tracker, though, and placed it down on the coffee table and sat down on the couch so you could take a better look at the grid. Gaster followed, studying the device’s screen. It was quite vague – there was no map or scale anything. Just six dots – that must have meant that there were six fragments in total. You suspected that the one with the X on it was the one you already had in the chamber.

So you had five to find. That seemed achievable. Still... “This is kind of tricky to interpret,” you gave Gaster a sidelong glance, “but at least we know where they are. Relative to us, anyway.” Gaster looked to be in thought for a bit, before writing something in the notebook.

**Perhaps the other two grey buttons can alter the formatting to make this clearer.**

You nodded – that definitely made sense. What else would the grey buttons be for? Gaster pressed the grey button in the middle, causing the screen to flash dark for a second before a series of numbers appeared on the screen. For a second, you were even more confused by this, but you realised that there were six different sets of numbers – probably corresponding to a soul piece each – that looked a little like coordinates. But... there were too many numbers in each set for them to be coordinates. 

Gaster seemed to know what they meant, though, because he perked up in recognition. He looked over to see your confusion, and took to the notebook to explain.

**They are coordinates. The first three numbers refer to depth or height, the second three to latitude, and the last three to longitude.**

“Oh, that’s perfect!” So you were right about them being coordinates. Only one of the sets of coordinates began with a negative number – you suspected therefore that that soul piece was underground. You grabbed your laptop so you could pull up Google Maps and start putting in the coordinates (the latitude and longitude, anyway) so that you could see exactly where in the world the other pieces were.

As you pinned each location, you began to understand just how spread out the pieces really were. “Well, the good news is that one of them is super close to where we are!” you told Gaster optimistically, turning the laptop to show him. “I think it’s the one with the negative depth coordinate. Must be in the Underground.” You mused, as you glanced back at the Soul Tracker’s screen to confirm that. Gaster studied the map as well, and agreed, signing “Yes, that seems correct.” The longer he looked at the map, however, the more apparent it became that he was realising the same thing you had realised.

Namely, that other than the piece that was (presumably) in the Underground and the piece you already had, the other four fragments were all in different countries entirely. Different _continents_ , in fact. Zooming in on each location, you noted down the countries they were in. Japan, Bolivia, Canada... even one in Libya. This was on a scale so much larger than you could ever have imagined. The shattering must have had an absolutely massive impact to throw the pieces of Gaster’s soul so far from the Underground, and so far from each other.

Gaster caught your attention before speaking to you through the notebook.

**I am still not wholly aware of the full size of the Surface world, but most of the pieces of my soul look to be great distances away from here.**

You nodded slowly. “Yeah, they are. It might be difficult to get to them, but at least we know where they are now. It’s a step closer.”

“You are right.” Gaster signed in agreement. He still looked distinctly hopeful that he would be able to restore his soul.

“In fact, the two of us could go to the Underground tomorrow to find the piece that’s down there.” You suggested. “I could go down under the guise of work and bring you down with me.”

“Yes, that sounds like a good idea.” Gaster signed excitedly at the prospect of being just a day away from having another piece of his soul restored.

You were excited too – but you couldn’t help but wonder how on Earth you were going to be able to travel across _continents_ to get the other four pieces. Only time would tell, you supposed. You would take it one day at a time.

**Notes for the Chapter:**

> So, we finally know where the soul pieces are now. Time to start putting them back together :D
> 
> Also – this was the end of the first arc of this story! Next chapter we move into the arc of soul-finding. 
> 
> Let me know what you guys thought of this one!


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